Bring a large pot of salted water to a boil. Cook the rigatoni according to package directions until al dente. Drain and set aside.
In a large skillet over medium heat, heat olive oil. Add sausage and cook until browned, breaking it up with a spoon as it cooks.
Add diced onion and sauté until softened, about 3-4 minutes. Stir in garlic, red pepper flakes, and Italian seasoning. Cook for 1 minute.
Pour in crushed tomatoes and season with salt and black pepper. Let it simmer for 8–10 minutes to thicken slightly.
Stir in heavy cream and Parmesan cheese. Mix until the sauce is creamy and combined.
Add cooked rigatoni to the skillet and toss until well coated in the sauce.
Garnish with fresh parsley and serve warm.