To your mince, add breadcrumbs, 2 cloves garlic, breadcrumbs, salt, parmesan, chilli flakes, your egg and 1 tbsp parsley. Mix well with your hands and form into 9 fat meatballs (about 90g each). Fry in oil until nicely browned and sealed on all sides. Add your marinara sauce and leave to bubble away on low heat for about 10 minutes.
Place the bottom half of your slider buns in a snug fitting tray and lay over sliced provolone. Add a meatball to each slider bun and top each with a tbsp of the sauce. Cover in mozzarella then top with the other half of the bun.
Mix your butter with the remaining parsley and garlic. Brush all over the buns.
Cover with foil and bake for 20 minutes at 350 fahrenheit. Remove the foil and bake for a further 10 minutes.