Combine beef, bread crumbs, onions, parsley, fresh minced garlic, egg, milk, chili powder, parmesan cheese, and a generous sprinkle of salt and pepper. Using your hands mix gently, careful not to over mix.Roll meat mixture into golf sized balls
Fry the meatballs in vegetable oil over medium high heat, working in batches. Brown them on all sides. Each batch should take about 7 minutes.
In a separate skillet or the same one warm up some marinara sauce
Place the browned meatballs in the sauce and let it cook for an hour or until the meatballs are tender and fully cooked through.
Place hero rolls cut side up on a baking sheet
Lay a couple of slices of provolone on the hero rolls
Add a couple of meatballs to the hero roll and ladle some marinara sauce over the meatballs
Sprinkle some mozzarella and parmesan cheese over the meatballs then place the sandwiches in a preheated oven at 400 degrees f for 5 minutes or until the cheese melts completely