A baked spaghetti squash casserole that swaps noodles for tender roasted squash strands, all layered with Italian sausage, marinara, and a generous amount of cheese. It’s a cozy, low-carb comfort meal you can pull together on a weeknight without much fuss.

What Makes This Casserole So Good

The roasted spaghetti squash gives you that familiar pasta-like feel, but it stays light and doesn’t weigh you down. Draining it well after roasting keeps the casserole from going watery, so every bite holds together.

Italian sausage brings a savory, fennel-forward richness that makes the whole dish feel substantial. I use a good jarred marinara to keep things quick, and the ricotta adds a creamy layer that reminds me of a baked ziti.

Then everything gets blanketed with mozzarella and Parmesan, baked until bubbly, and broiled for a minute so the top gets crispy brown edges. It’s the kind of casserole that gets quiet at the dinner table.

Ingredients

1 medium spaghetti squash (about 3 lbs): look for a firm, heavy squash with no soft spots
1 tbsp olive oil: for roasting the squash
1 lb mild or hot Italian sausage: casings removed; use hot if you like a little kick
2 cloves garlic, minced
2 cups marinara sauce: your favorite jarred variety or homemade
1 cup full-fat ricotta cheese: full-fat avoids a grainy texture once baked
1 1/2 cups shredded low-moisture mozzarella: divided
1/4 cup grated Parmesan cheese
1/2 tsp kosher salt
Freshly ground black pepper: a few good cracks

Variations and Substitutions

Ground turkey or chicken: brown it the same way; add a pinch of fennel seeds to mimic the sausage flavor
Vegetarian: skip the meat and sauté 8 oz sliced mushrooms in olive oil before adding the marinara
Dairy-free: use a thick cashew ricotta and a good melting plant-based mozzarella, plus a nutritional yeast sprinkle instead of Parmesan
Extra greens: fold a few handfuls of fresh baby spinach into the filling right before assembling

This recipe has the same cozy spirit as a classic Zucchini Lasagna if you want to try another baked squash dish.

How to Make Cheesy Spaghetti Squash Casserole with Italian Sausage

Step 1: Roast the Squash

Preheat the oven to 400°F (200°C). Cut the spaghetti squash in half lengthwise and scoop out the seeds. Drizzle the cut sides with the 1 tablespoon olive oil and rub it in, then season the squash with a pinch of salt and a few grinds of black pepper.

Place both halves cut side down on a baking sheet and roast for 30 to 40 minutes. You’ll know it’s ready when the skin gives slightly under pressure and a fork slides into the flesh without resistance. Flip them over and let the squash cool just enough to handle, then drag a fork through the flesh to create long, noodle-like strands. Transfer the strands to a colander and press gently with a spoon to release any excess liquid. Draining here is the secret to a casserole that isn’t soupy.

Step 2: Brown the Sausage

While the squash roasts, warm a large skillet over medium heat. Add the 1 pound Italian sausage and cook, breaking it up with a wooden spoon, until it’s deeply browned and cooked through, about 5 to 7 minutes. If your sausage releases a lot of fat, spoon off all but a thin coating so the casserole isn’t greasy.

Stir in the minced garlic and cook just until fragrant, about 30 seconds. Pour in the 2 cups marinara sauce, reduce the heat to low, and let it simmer gently while you assemble the rest, around 10 minutes. The sauce will thicken slightly and the whole kitchen will smell like a Sunday dinner.

Step 3: Mix the Filling

In a large bowl, combine the drained spaghetti squash strands, the 1 cup ricotta, half of the shredded mozzarella (about 3/4 cup), the 1/2 teaspoon salt, and several cracks of black pepper. Fold everything together with a rubber spatula or your hands until the cheese is evenly distributed and the squash picks up a pale, creamy coating. The mixture will look a little messy, that’s fine.

Taste a small strand at this point and adjust the salt or pepper. Since the marinara and sausage already carry some seasoning, a light hand is all you need.

Step 4: Assemble and Bake

Spoon the squash filling into a 9×9 inch baking dish (or something similar in size) and spread it into an even layer. Pour the sausage and marinara mixture right on top, then use the spatula to gently swirl it into the squash so every bite gets both. Scatter the remaining mozzarella and the 1/4 cup Parmesan evenly across the surface.

Bake at 375°F (190°C) for 20 to 25 minutes. The casserole is done when the sauce is bubbling around the edges and the cheese on top has melted into a glossy layer. The center should feel set when you jiggle the dish.

Step 5: Broil and Serve

Switch the oven to broil on high. Slide the dish back in on an upper rack and watch it closely. After 2 to 3 minutes the cheese will turn deep golden brown in spots and get those craggy edges that make a casserole look like it means business.

Pull the dish out, let it rest on the counter for 5 minutes so the layers settle, then scoop big spoonfuls onto plates. Serve while it’s still hot and the cheese stretches.

A Few Things to Keep in Mind

Squeeze the squash well after shredding. I like to pile the strands in a clean kitchen towel and twist it over the sink to get rid of as much water as possible. The drier the squash, the richer the casserole tastes.
Use hot Italian sausage if your family likes a little heat. The spice mellows in the sauce but leaves a pleasant warmth behind.
Don’t skip the broil step. It only takes a couple of minutes and gives the top that blistered, almost pizza-like finish.
If you want to make this in one pan, use an oven-safe skillet to brown the sausage, mix everything in, and bake right in the skillet.

Bake times by dish size:

Dish size	Bake time at 375°F
8×8 or 9×9 inch	20 to 25 mins
Oval 2-qt baker	25 to 30 mins
9×13 inch (1.5x recipe)	30 to 35 mins

Storing and Reheating Leftovers

Refrigerate: Store any leftovers in a sealed container for up to 4 days. The flavors actually blend nicely overnight.
Reheating: Warm individual portions in the microwave for 1 to 2 minutes, or cover the whole dish with foil and heat in a 350°F oven until warmed through, about 15 minutes. A quick hit under the broiler at the end can revive the crispy top.

What to Serve with This Casserole

A simple green salad with a sharp vinaigrette cuts through the richness of the cheese and sausage nicely. For a little crunch on the side, garlic bread works beautifully, or go low-carb with a batch of almond flour biscuits. Roasted broccoli tossed with lemon zest and red pepper flakes rounds out the meal without making it feel heavy.

Frequently Asked Questions

Can I use cottage cheese instead of ricotta?

Yes, use full-fat small curd cottage cheese in the same amount. Blitz it briefly in a food processor first for a smoother texture.

How do I make this casserole ahead of time?

Assemble the whole dish without baking, cover, and refrigerate for up to 24 hours. When you’re ready to eat, bake it straight from the fridge, adding about 5 extra minutes to the bake time.

Why did my casserole turn out watery?

Squash naturally holds a lot of moisture. Roasting cut side down releases some steam, but the most important step is giving the strands a thorough press and drain before mixing with the other ingredients. A quick squeeze in a towel fixes almost any wateriness problem.

Can I freeze leftovers?

Yes, the baked casserole freezes well. Wrap individual portions tightly and freeze for up to 2 months. Thaw overnight in the fridge and reheat in the oven or microwave.