In a large skillet, cook beef and onion over medium heat until meat is no longer pink; drain. Stir in the tomato sauce, macaroni, Italian seasoning, garlic powder and pepper. Bring to a boil. Reduce heat; cover and simmer for 15-20 minutes or until macaroni is tender.
Sprinkle with cheese. Cover and cook for 2-3 minutes or until cheese is melted. Serve.