Place frozen meatballs (no need to thaw them) and marinara sauce in a saucepan. Stir to coat meatballs with the marinara sauce.
Place lid on the pan and cook on low for about 10-15 minutes, stirring occasionally until meatballs and sauce are heated through. Remove from heat and keep warm.
While meatballs and sauce are heating up on the stove, prepare the rolls.
Using a serrated knife cut loaves in half horizontally. Use your fingers and pull out bread from the center creating a well that will hold the meatballs.
Line each hollowed out half of bread with slices of Mozzarella cheese.
Place in the oven and broil until cheese is melted and edges of bread is toasted golden brown.
Cut each meatball in half and divide meatball pieces evenly among toasted hoagie rolls.
Spoon marinara sauce over meatballs.
Top with grated Parmesan cheese.
Sprinkle sandwiches with Italian seasoning.
Carefully place halves together and cut sandwiches down the center to serve.
Serve with loads of napkins.