Preheat oven to 375°F (190°C).
In a mixing bowl, combine ground beef, breadcrumbs, beaten egg, minced garlic, grated Parmesan, salt, and black pepper. Mix well.
Form the mixture into meatballs, about 1 inch in diameter.
Heat a frying pan over medium heat and cook the meatballs until browned on all sides.
Place the meatballs in a baking dish, cover with marinara sauce, and bake in the preheated oven for 20 minutes.
Toast the hoagie rolls in the oven for a few minutes until lightly browned.
Assemble the sandwiches by placing meatballs and sauce on the toasted hoagie rolls, then top with shredded mozzarella cheese.
Return the assembled sandwiches to the oven for a few minutes until the cheese is melted.