Cheeseburger Pizza

1 pound lean ground beef
1 large pizza shell (Boboli)
1 cup pizza sauce
1 cup shredded Cheddar cheese
1 cup shredded mozzarella cheese
12 frozen onion rings (or more)

Brown the ground beef and drain off fat. Place bread shell on a baking pan. Spread the shell with the pizza sauce. Top with the cheeses, beef and onion rings. Bake at 425 degrees F for 12 to 15 minutes or until the onion rings are browned.