Preheat oven to 375. Coat six 10 to 12 oz. individual casseroles with cooking spray. Set aside. Cook pasta as pkg. directs. Drain. Meanwhile, cut pepperoni slices into quarters and set aside.
In large skillet, cook ground beef and onion over medium heat til meat is brown and onion is tender, using a wooden spoon to break up meat as it cooks. Drain off fat. Stir pasta sauce, shredded cheese, cooked pasta and pepperoni into meat mixture in skillet.
Divide meat mixture evenly between prepared casseroles. Unroll pizza crust and cut into 6 equal size pieces. Place one piece over dishes to make rounded tops. Bake for 25 to 30 minutes or til pizza dough is golden brown. Let stand 5 minutes. Carefully invert each casserole to serve. If desired, sprinkle with grated Parmesan cheese. make 6 servings.