Preheat the oven to 350 degrees.
Soften the butter slightly in the microwave and mix with the 2 tsp garlic powder.
Slice open the Hoagie rolls, but don't fully cut them in half.
Split them apart just enough that you can spread a light layer of the garlic butter mixture on each side.
Place 3-4 meatballs in each roll, top with about 1/4 -1/2 cup of sauce.
Top each with mozzarella and place on a parchment paper lined cooking tray (or else use cooking spray).
You can use the rolls to support each other so they don't fall over spilling all their yummy goodness OR you could also use a shallow baking pan to help them stay put.
Bake until the cheese gets melty and the rolls start to look a little brown and crispy (about 10 -12 minutes).