Preheat your air fryer to 380°F (193°C).
In a large bowl, mix together the ground beef, bread crumbs, Parmesan cheese, chopped parsley, egg, garlic powder, salt, and pepper until fully combined.
Form the mixture into 12-16 meatballs.
Place the meatballs in the air fryer basket in a single layer, making sure they are not touching.
Air fry the meatballs for 8-10 minutes or until they are browned on all sides and fully cooked through, shaking the basket halfway through.
Pour the marinara sauce into a medium-sized saucepan and heat it over medium heat until simmering.
Cut the hoagie rolls in half lengthwise and place them on a baking sheet.
Add 4 meatballs (or 3 if you only made 12) into each roll.
Spoon some of the marinara sauce over the meatballs, then sprinkle shredded mozzarella cheese over the top.
Place the baking sheet in the oven under the broiler for 1-2 minutes, or until the cheese is melted and bubbly.
Remove from the oven and let cool for a few minutes before serving.