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.

Add the beef, pork, onion, garlic, Parmesan cheese, breadcrumbs, eggs, milk, Italian seasoning, and crushed red pepper flakes, if using, to a large mixing bowl. Season 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 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 form the meat around 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.

Note: The meatballs will reach a safe temperature of 165°F while they rest and are warmed in the marina sauce.

Remove the baking sheet from the oven and set aside, but do not turn off the oven.

Pour the marinara sauce into a large skillet set over medium-low heat and carefully add the meatballs. (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 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 meatballs and some of the sauce. Top each sub with two or three slices of Provolone cheese and place in the oven until the cheese is melted, approximately 3-5 minutes.

Remove from oven and serve immediately with your choice of sides. Enjoy!