Preheat oven to 400°F and a broiler.

Scatter pumpkin seeds on a baking sheet and sprinkle with sugar, chili powder and cinnamon. Roast for about 30 minutes, until golden brown, and set aside.

Place pumpkin quarters on a baking sheet and roast for about 30 minutes, until tender. Once cool enough to handle, scoop the flesh out of the quarters and transfer it to a food processor. Pulse until smooth.

Place a large pot of salted water over high heat to boil. When water is boiling, drop tortellini and cook to al dente according to package directions. Drain cooked tortellini and reserve.

While the pasta water is heating up, place a large skillet over medium-high heat with 2 tablespoons of butter. Once the butter has melted, add the onion and garlic, and season with salt and pepper. Sauté for 4-5 minutes, until the onions soften.

Sprinkle in the flour and cook about a minute. Whisk in the milk and cook until the liquid comes up to a bubble and the sauce thickens, 2-3 minutes. Stir in the nutmeg and reserved pumpkin puree. Season with salt and pepper and simmer until thickened, about 1 minute.

When everything is ready, toss the tortellini with the pumpkin sauce and transfer to a casserole dish. Cover with the cheese and pop under the broiler until brown and bubbly, about 2 minutes. Serve roasted pumpkin seeds alongside the tortellini lasagna.