Preheat oven on broil
If your meatballs are not coming straight out of the oven, cut them in half and heat them in a frying pan with 1 1/2 cups tomato sauce.
Meanwhile, add 1 tablespoon oil and minced garlic clove to a frying pan, cook on medium low until fragrant
Add 1 cup sliced onions and 1 cup peppers to the pan and season with salt and pepper and 1/4 teaspoon dried basil, cooking until al dente, about 10 minutes
Slice open your buns and place flat on a covered baking sheet (parchment or foil will work).
Spoon sauce on one half, and add about three meatball halves on top. Top with more sauce.
Add veggies to the other side of the bun and cover with shredded mozzarella cheese.
Place baking sheet into oven, about 5 minutes, or until cheese is melted and bubbling.
Remove from oven, fold like a sandwich and enjoy!