Preheat oven to 375°F (190°C).
In a mixing bowl, combine ground beef, breadcrumbs, egg, garlic powder, onion powder, salt, and black pepper. 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 hoagie rolls and top with marinara sauce and shredded mozzarella cheese.
Place the sandwiches on a baking sheet and bake in the oven for an additional 5-10 minutes, or until the cheese is melted and bubbly.
Serve hot and enjoy!