Preheat oven to 375 degrees F (190 degrees C). Grease a 9x13-inch baking dish.
Bring a large pot of lightly salted water to a boil; cook the rotini at a boil until tender yet firm to the bite, about 8 minutes; drain.
Cook and stir sausage in a skillet over medium heat until browned and crumbly, 5 to 10 minutes. Drain sausage on paper towels and reserve 2 tablespoons grease in the skillet. Add oil to grease in the skillet; cook and stir onion, garlic, and red pepper flakes in the hot oil-grease until onion is soft, about 3 minutes.
Stir chicken broth, pumpkin, bacon, Italian seasoning, and salt into onion mixture; bring to a boil. Lower heat and simmer for 5 minutes. Stir cream and sausage into broth mixture and simmer until creamy and thickened, about 5 minutes. Add rotini and gently toss. Transfer mixture to the prepared baking dish and top with Parmesan cheese.
Bake in the preheated oven until bubbling and golden brown, about 35 minutes.