Preheat oven to 425 degrees. Spray 4 quart baking dish with nonstick cooking spray.
Prepare pasta according to package directions. Reserve 1/2 cup pasta cooking water and set aside for later use. Drain pasta and return to pot.
Cook Italian chicken sausage. Cut into 1/4 inch pieces or smaller and set aside.
Combine pumpkin, flour, garlic powder, salt, nutmeg and cayenne pepper in medium skillet over medium heat. Slowly add evaporated milk, stirring until smooth. Cook, stirring, for 2 to 3 minutes until mixture begins to thicken. Pour over pasta in pot. Add sausage and reserved pasta cooking water.
Spread half of the pasta mixture into prepared dish. Top with spinach. Add remaining pasta mixture. Lightly spray piece of foil with nonstick cooking spray. Cover dish with greased side down. Bake for 20 minutes until heated through
Combine mozzarella and parmesan cheeses and sprinkle on top of casserole. Bake uncovered for an additional 5 minutes until cheese is melted.