1. Preheat the oven to 375 degrees F. Line a large rimmed baking sheet with heavy-duty aluminum foil. Spray the foil with nonstick cooking oil spray. Have a 9" x 13" or similar-size baking dish at hand.
2. Combine the squash and onion pieces with the nutmeg, the salt and pepper to taste and the olive oil on the prepared sheet; toss to mix. Arrange the seasoned vegetables in a single layer and transfer the sheet to the oven. Roast for 35 to 40 minutes, until the squash is tender and the onion has browned lightly. Remove the vegetables from the oven; reduce the temperature to 350 degrees .
3. While the vegetables roast, cook the pasta according to the package directions. Drain.
4. Combine 1 1/2 cups of the ricotta with 2 tablespoons of the Parmesan cheese in a large bowl; add salt and pepper to taste. Add the cooked pasta and toss to incorporate.
5. Add the roasted vegetables to the bowl and gently mix to combine. Transfer the mixture to the baking dish. Drop dollops of the remaining 1/2 cup of ricotta over the pasta. Use a small knife to spread out the dollops; they will not cover the pasta completely. Sprinkle the remaining 1 tablespoon of Parmesan cheese over the dish. Cover with aluminum foil and bake for 15 to 20 minutes, or until heated through. For a more finished look: After the pasta has baked, turn on the broiler, uncover the pasta and broil for 3 to 4 minutes, until the cheese has lightly browned.