To make these sandwiches, start by preparing the meatballs. Add all of the meatball ingredients to a large bowl (the ground beef, ground pork, breadcrumbs, yellow onion, parsley, garlic, parmigiano reggiano, eggs, allspice, kosher salt, and ground black pepper) to a bowl and use your hands to mix them together until they're fully combined.
Next, divide the mixture into 16 meatballs and roll them until they're perfectly round. Line them up on a baking sheet, then repeat until all of the meatballs have been formed.
Heat a large skillet, on the stove, over medium-high heat, and pour in the marinara sauce.
Once the sauce reaches a simmer, add the meatballs to the pan and place the cover on top.
Allow the meatballs to cook, undisturbed, for 25 minutes.
Once the 25 minutes are up, remove the cover and stir to coat all of the meatballs in the sauce. Remove them from the heat, and allow them to sit while you prepare the rest of the sandwiches.
Next, preheat your oven to 350 F.
Cut open the french rolls in half, being careful not to break them or cut them all the way through. You should create a nice, deep pocket in the rolls.
Next, add 3 meatballs to each roll and spoon some of the marinara sauce on top.
Then, add a slice of provolone to the top of the meatballs.
Brush the sides of the rolls with some melted butter or olive oil. Repeat the above steps until all of the rolls have been formed!
Then, transfer the rolls into the oven and allow them to bake for 5-10 minutes, or until the cheese has fully melted and the bread has lightly browned. You can turn on the broiler for 1 minute at the end, to get the bread nice and crispy, but be sure to watch it carefully so that it doesn't burn.
Once the sandwiches are done, remove them from the oven.
Garnish with a sprinkle of fresh parsley, then serve and enjoy!