1Heat oven to 375°F. Spray 12 regular-size muffin cups with cooking spray.
2In large bowl, mix ground beef, oats, onion, salt, pepper and egg with hands or spoon. Using 1/4-cup measuring cup, scoop beef mixture into each muffin cup; press into cup.
3Make indentation in center of mixture in each cup. Spoon 1 tablespoon cheese into each indentation. Top each with 1 tablespoon desired topping.
4Bake 35 minutes or until meat thermometer inserted in center of loaves reads 160ºF. Remove from muffin cups. If desired, top with additional topping before serving.