Combine the ground beef, onion, breadcrumbs, parmesan cheese, egg, Italian seasoning, garlic powder and chopped parsley in a large bowl. Mix everything together with your hands until well combined.
Divide and shape the mixture into ten meatballs. Air-fry the meatballs for 10 minutes turning over half way through the cooking time.
Slice open the hoagie rolls and spread a little marina sauce inside. Place two slices of the provolone cheese over the sauce. Top the cheese with three meatballs per hoagie roll and a little additional sauce. Top with two more slices of provolone cheese and return the sandwiches to the airfryer, one or two at a time, to melt the cheese and toast the bread.
In a large bowl, combine and stir the first 10 ingredients.
Include beef mix gently however completely.
Press into balls about 4cm in diameter.
In batches, arrange meatballs in a single layer on greased tray in airfryer basket. Cook until they are lightly browned and cooked through, 12-15 minutes.
Meanwhile, in a small saucepan, combine sauce ingredients.