Preheat the oven to 375°F (190°C).
In a large bowl, combine ground beef, breadcrumbs, Parmesan, egg, garlic, parsley, Italian seasoning, salt, and pepper.
Shape the mixture into small meatballs, about 1 inch in diameter.
Arrange the meatballs on a lined baking sheet and bake for 20 minutes.
While the meatballs are baking, gently heat the marinara sauce in a saucepan over low heat.
Remove the meatballs from the oven and place them in the warmed marinara sauce.
Slice the rolls in half and place a meatball inside each roll, spooning extra sauce over the top.
Top each meatball with shredded mozzarella cheese and return to the oven for an additional 5-7 minutes, or until the cheese is melted and bubbly.
Serve warm, garnished with extra parsley if desired.