Mix together all ingredients from ground beef through pizza sauce.
Separate the halves of the hamburger buns, placing each half face-up on a baking sheet.
Spread the meat mixture on each of the hamburger bun halves. (I have found the fastest way to do this is using Pampered Chef's medium scoop and dividing the meat mixture between the bun halves; then, using the back of a large soup spoon, smooth the meat mixture evenly over the bun.).
Top each with a slice of mozzarella.
Bake for 20 minutes or until the cheese is golden and bubbly.