Preheat oven to 375°F (190°C).
In a mixing bowl, combine ground beef, breadcrumbs, egg, garlic, salt, pepper, and Parmesan cheese. Mix well.
Form the mixture into meatballs and place them on a baking sheet.
Bake the meatballs in the preheated oven for 20 minutes or until cooked through.
While the meatballs are baking, warm the marinara sauce in a saucepan over medium heat.
Once the meatballs are done, place them in the marinara sauce and let simmer for 5 minutes.
Toast the hoagie rolls in the oven for 5 minutes or until slightly crispy.
Assemble the sandwiches by placing meatballs and sauce on each hoagie roll and topping with shredded mozzarella cheese.
Serve hot and enjoy!