This spaghetti squash casserole is rich, creamy, cheesy and delicious. It’s a great addition to your holiday table that everyone will enjoy. Spaghetti squash is frequently used as a side dish, but this casserole is hearty enough to be main event!

cheesy spaghetti squash casserole with sausage and spinach in baking dish

This is one of my favorite recipes. I feel like I say that a lot, don’t I? Spaghetti squash is so fun to cook with because it really looks like strands of spaghetti!

And it not only looks like spaghetti, but it also has something else in common with pasta. Like pasta, it’s basically a blank canvas to which you can add many different flavors, herbs, spices and other seasonings. It’s extremely versatile. And it’s a great way to get the pasta experience if you’re cutting back on your carbs!

Ingredients & Substitutions

cheesy spaghetti squash casserole with sausage and spinach ingredients

Spaghetti squash: Spaghetti squash is probably the coolest squash. Is it a squash or is it spaghetti? It’s both! No other squashes can say that.
Italian sausage: I used sweet Italian sausage, but hot Italian sausage, or other types of sausage would be delicious.
Cream: Adds a richness to the casserole.
Egg: I used one large egg.
Onion: I like the layer of flavor onions add to the dish. I have a family member that can’t eat onions, so I’ve made this without, and it tasted great.
Spinach: Defrost the frozen spinach and squeeze out all the liquid.
Cheese: I used grated Swiss cheese and I’ve also used mozzarella and gruyère. Any melty cheese would work here – fontina, gouda, shredded Italian blend.
Sage and thyme: I love these two herbs. They taste like fall.
Parmesan: Sometimes I use parmesan and other times I’ll use Parmigiano-Reggiano.

How to Make Spaghetti Squash Casserole

scooping seeds and pulp from spaghetti squash with spoon

Preheat the oven to 400°F.
Cut the spaghetti squash in half. Make sure you’re on a sturdy surface and be very careful!
Using a large spoon, scoop out the seeds and pulp. Don’t throw the seeds away! See my recipe for roasted squash seeds.

spaghetti squash on baking sheet cut side up

spaghetti squash on baking sheet face side down

Drizzle olive oil over the squash and use your hands to cover the entire cut-side (not the skin) of the squash with olive oil. Season each half with salt and pepper.
Place the squash halves face side down on a baking sheet.
Roast in the oven for about 35-45 minutes or until tender, when the tip of paring knife can easily be slipped into flesh. The time will vary depending on the size of your squash.

Remove the squash from the oven. Flip the squash halves so the cut side is facing up and let cool.
Once the squash is cool, use a fork to separate the squash into strands.
Put squash strands in a strainer over a large bowl to drain off any excess moisture.

Reduce the oven temperature to 350°F.
Add the sausage and onions to a large skillet over medium-high heat. Cook until the sausage is cooked through, and the onions are lightly browned, about 5 to 7 minutes, breaking up the sausage with a wooden spoon or a spatula.
Transfer the sausage and onions to bowl and set aside. Pour off any fat from the skillet.
Add the spaghetti squash strands and the spinach to the skillet. Cook until most of the moisture has been removed, about 5-8 minutes. I do this extra step to make sure most of the moisture has been cooked out of the squash and spinach.
Remove from the heat and let cool for a couple minutes.

spaghetti squash casserole ingredients in bowl

spaghetti squash casserole ingredients mixed together in bowl

While the squash mixture is cooling, spray a 9 x 13-inch baking dish with cooking spray.
In a large bowl, mix together the cream, egg, sage, thyme, cheese, salt and pepper.
Add the sausage, onions, squash and spinach to the bowl and mix to combine.
Pour the squash mixture into the prepared baking dish.
Bake at 350°F for 30-35 minutes or until cooked through and the cheese is nicely browned.

spaghetti squash casserole on spoon closeup

Expert Tips

Make it vegetarian – Use a plant-based sausage of your choice. I love the Field Roast Italian-garlic and fennel sausages and that’s what I use when making this vegetarian.
Don’t throw out the seeds! – Save squash seeds and roast them for a delicious snack! I show you how to do it in my roasted squash seeds recipe.
Squeeze the spinach – It’s important to squeeze as much of the liquid from the spinach that you can so the casserole isn’t mushy. I put the thawed spinach in the center of a clean dish towel and wrap the towel around it. Wring the towel over the sink to squeeze the liquid from the spinach.
Safety when cutting the squash – Rest the squash on a towel when cutting it open so it doesn’t slide around. Start small with a paring knife and make a cut down the center of the squash. Remember to cut away from your other hand so if the knife slips you don’t cut yourself. After you’ve scored the squash, use a chef’s knife to finish the job, cutting all the way through the squash.

Variations

Cheese it up! – I don’t usually measure the amount of cheese I’m putting on or in this dish (but I had to do so to write this recipe), and I’m assuming that I use a lot more cheese. So feel free to break the rules and use more cheese! And play around with different cheeses. I’ve used gruyere and mozzarella, but other cheeses would be good too!
Different herbs – Try other herbs or spices in this casserole, like oregano, basil, parsley or rosemary. Use fresh herbs instead of dried herbs (substitute 1 Tbsp of fresh herbs for every 1 tsp of dried).
Add-ins and toppings – Top it with breadcrumbs or sprinkle some crushed red pepper on top. Throw in some sun-dried tomatoes or mix in some pesto.
Change up the greens – Swap out the spinach for other greens, like kale or chard.

Can I Make This Ahead of Time?

You can cook the spaghetti squash and store in an airtight container for up to 4 days. The sausage and onions can be cooked a couple of hours before assembling the casserole.

How to Store Spaghetti Squash Casserole

This casserole can be stored in an air-tight container in the refrigerator for 3-4 days. Depending on how much is left (and how much room I have in the refrigerator), I usually throw some plastic wrap over the baking dish and put the whole thing in the fridge.

I haven’t tried freezing this casserole because spaghetti squash can get watery when it thaws out, so I wouldn’t recommend freezing it. If you have a technique for freezing spaghetti squash, please share it in the comments!

Other Recipes You’ll Love

Cheesy Spaghetti Squash Casserole with Sausage and Spinach

This spaghetti squash casserole is rich, creamy, cheesy and delicious. It's a great addition to your holiday table!

5 from 6 votes

Print Recipe Pin Recipe

Prep Time 25

Cook Time 1 20

Total Time 1 45

Servings

Ingredients

1 3-3½ lb spaghetti squash
1-2 tsp olive oil
3 sweet Italian sausages
1 cup onion, diced
8 oz spinach, frozen
1 ½ cup Swiss cheese, grated
1 cup heavy cream
1 egg, large, beaten
½ tsp dried sage
½ tsp dried thyme
½ tsp salt
¼ tsp fresh ground black pepper
1/2 cup parmesan cheese

Instructions

Preheat oven to 400°F.
Cut spaghetti squash in half. Using a large spoon, scoop out seeds and pulp.
Drizzle olive oil over squash and use your hands to cover the entire cut-side (not the skin) of squash with olive oil. Season with salt and pepper.
Place squash halves face side down on baking sheet.
Roast in oven for about 35-45 minutes or until tender, when the tip of paring knife can easily be slipped into flesh.
Remove squash from oven. Flip squash halves so the cut side is facing up and let cool.
Once squash is cool, use a fork to separate squash into strands.
Put squash strands in a strainer over a large bowl to drain off any excess moisture.
Reduce oven temperature to 350°F.
Add sausage and onions to a large skillet over medium-high heat. Cook until sausage is cooked through, and onions are lightly browned, about 5 to 7 minutes, breaking up sausage with a wooden spoon or a spatula.
Transfer sausage and onions to bowl and set aside. Pour off any fat from skillet.
Add the spaghetti squash strands and the spinach to the skillet. Cook until most of the moisture has been removed, about 5-8 minutes.
Remove from heat and let cool for a couple minutes.
While squash mixture is cooling, spray a 9 x 13-inch baking dish with cooking spray.
In a large bowl, mix together the cream, egg, sage, thyme, cheese, salt and pepper.
Add sausage, onions, squash and spinach to bowl and mix to combine.
Pour squash mixture into prepared baking dish.
Bake at 350°F for 30-35 minutes or until cooked through and the cheese is nicely browned.

Notes

Don’t throw out the seeds! – Save squash seeds and roast them for a delicious snack! I show you how to do it in my roasted squash seeds recipe.

Squeeze the spinach – It’s important to squeeze as much of the liquid from the spinach that you can so the casserole isn’t mushy. Put the thawed spinach in the center of a clean dish towel and wrap the towel around it. Wring the towel over the sink to squeeze the liquid from the spinach.

Safety when cutting the squash – Rest the squash on a towel when cutting it open so it doesn’t slide around. Start small with a paring knife and make a cut down the center of the squash. Remember to cut away from your other hand so if the knife slips you don’t cut yourself. After you’ve scored the squash, use a chef’s knife to finish the job, cutting all the way through the squash.

Nutrition

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