1. Cook rigatoni in salted boiling water until al dente. Drain and set aside.
2. Heat olive oil in a skillet over medium heat. Add onion and cook until softened, about 3 minutes.
3. Add garlic and ground beef. Cook until beef is browned, breaking it apart as it cooks. Drain any excess fat.
4. Stir in marinara sauce, salt, and pepper. Simmer on low for 10 minutes to blend flavors.
5. Toss the cooked rigatoni with the meat sauce until well-coated.
6. Serve warm, topped with grated Parmesan cheese.