In a large pot, bring salted water to a boil. Add the rigatoni pasta and cook according to package instructions until al dente. Drain and set aside.
In a large skillet, heat the olive oil over medium heat. Add the diced onion and sauté for about 2-3 minutes until translucent.
Add the sausage to the skillet, breaking it apart with a wooden spoon. Cook for 5-7 minutes or until browned and cooked through.
Stir in the minced garlic and cook for another 1-2 minutes until fragrant.
Lower the heat and pour in the heavy cream. Stir until well combined, then add the Italian seasoning, salt, and black pepper. Allow the sauce to simmer for about 5 minutes until it thickens slightly.
Mix in the grated Parmesan cheese, stirring until it melts into the sauce.
Add the cooked rigatoni to the skillet, tossing it in the creamy sauce until evenly coated.
Serve hot, garnished with freshly chopped parsley.