Preheat oven to 425F.
Bring a large pot of salted water to a boil. Add the cauliflower and boil for about 3-5 minutes or until easily pierced with a fork. Use a fine mesh strainer or spider strainer to transfer the cauliflower to a high-speed blender. Then add the pasta to the boiling water and cook to al dente. Reserve about 1 cup pasta water before draining.
Wipe the pot dry, then warm the oil over medium heat (you can also do this in a small skillet while the pasta boils). Add garlic, rosemary, pepper, and nutmeg and cook, stirring often, for about 45 seconds. Transfer to the blender, scraping out all of the oil and contents. Add the pumpkin, cottage cheese, 1 teaspoon salt, and ½ cup of the reserved pasta water (or just use regular water if you forgot) and blend until totally smooth. If it’s not blending easily, add a bit more pasta water.
In a 9x13-inch baking dish, pour in half of the pumpkin mixture and spread it around/give the pan a shake to create an even layer. Then add the pasta and spread it into an even layer. Sprinkle 1 cup of the gouda, fontina, or mozzarella cheese over top, and then pour the remaining puree evenly over top. Give it a shake again and use a spoon to spread it around, then top with remaining 1 cup cheese and parmesan. Grate some black pepper over top, if you’d like.
Cover with foil and bake for 10 minutes, then remove the foil and bake for 15 more minutes, or until the cheese is lightly browned and bubbly on top. Let cool for about 10 minutes, then serve topped with fresh parsley and a squeeze of lemon (if using).