In a large skillet brown the ground beef until no longer pink, drain.
Add onion and saute for a couple minutes.
Remove from heat.
Add pizza sauce and salt and pepper.
Scoop beef mixture on half a bun, using about 1/3 cup beef mixture per bun.
Repeat for remaining buns placing buns on a cookie sheet.
Top all buns with a slice of mozzarella cheese .
Place pepperoni or favorite pizza toppings on top of cheese.
Sprinkle with oregano and Parmesan cheese.
Broil in the oven until cheese is melted.