Preheat oven to 400, setting the rack in the upper third of the oven. In a large bowl, combine everything except the marinara and the Mozzarella. Lightly mix together, using hands or a large spoon. Scoop and shape into small meatballs and place fairly close together on a foil lined baking sheet. Spoon about a half Tbsp of sauce over each meatball. Bake 15 minutes.

Remove meatballs from oven and increase temperature to broil. Spoon an additional half Tbsp of sauce over each meatball and top with a small square of Mozzarella. Broil an additional 3 minutes, until the cheese has melted and turned golden. Serve with additional sauce.