1Cook and drain macaroni as directed on package.
2Meanwhile, in 12-inch skillet, cook beef and onion over medium-high heat 5 to 7 minutes, stirring frequently, until beef is brown; drain. Stir in macaroni, pepperoni, mushrooms and pizza sauce.
3Cover and cook over medium heat 8 to 10 minutes, stirring occasionally, until hot. Remove from heat. Sprinkle with cheese. Cover and let stand 2 to 3 minutes or until cheese is melted.