• Place the top oven rack in the center position and pre-heat oven to 400°F. Spray a large, rimmed cookie sheet with non-stick cooking spray and set aside.
• Get a large bowl then add the beef, pork, onion, garlic, Parmesan cheese, bread crumbs, eggs, milk, Italian seasoning, and crushed red pepper flakes, if using. Season it with salt and black pepper, to taste.
• Combine thoroughly with clean hands until all ingredients are thoroughly incorporated into the mixture. Do not overwork.
• Transfer the mixture from the large mixing bowl to a clean work surface and spread into a uniformly thick rectangle and cut into 12 equal-sized portions, as shown.
• Divide the cheese sticks evenly between the 12 squares and place at the center of each meatball. For the cheese firmly with your hands to create the meatballs. Place the finished meatballs on the prepared baking sheet. Repeat with remaining sections until complete.
• Place the baking sheet on the top oven rack for 10 minutes. Remove from oven and carefully turn each meatball with a spatula. Return to oven and bake for another 8-10 minutes, or until an instant read thermometer reads 160°F when inserted into the thickest part of the meatballs.
• Remove the baking sheet from the oven and set aside, but do not turn off the oven.

Arranging Your Cheese-Stuffed Meatball Subs

• Pour the marinara sauce into a large skillet set over medium-low heat and carefully place meatballs in it. (Remove any excess grease off the meatballs with paper towels first). Simmer for 4-5 minutes, or until the sauce is heated through, while carefully turning the cheesy stuffed meatballs to coat in the sauce.
• Carefully slice open the hoagie buns and arrange on a lined baking sheet. Fill each bun with two or three cheesy meatballs and some of the sauce. Get two or three slices of Provolone cheese and put it on top of the meatball sub. Place them in the oven until the cheese is melted, approximately 3-5 minutes.
• Remove from oven and serve immediately with your choice of sides. Enjoy!