Creating Meatball Sub Sandwiches is simple and rewarding. Follow these steps for delicious results:

1. Preheat the Oven: Preheat your oven to 375°F (190°C).
2. Prepare Meatball Mixture: In a large bowl, combine ground beef, breadcrumbs, Parmesan cheese, parsley, egg, garlic, salt, and pepper. Mix until well combined.
3. Form Meatballs: Shape the mixture into meatballs, about 1 to 1.5 inches in diameter. Place them on a baking sheet lined with parchment paper.
4. Bake Meatballs: Bake the meatballs in the preheated oven for about 20 minutes, or until cooked through and browned.
5. Heat Marinara Sauce: While the meatballs are baking, heat the marinara sauce in a saucepan over medium heat. Once warmed, add the cooked meatballs to the sauce, stirring gently to coat.
6. Prepare Hoagie Rolls: Slice the hoagie rolls open without cutting all the way through. Place them on a baking sheet.
7. Assemble Sandwiches: Spoon meatballs and marinara sauce into each hoagie roll, ensuring each roll gets a generous portion.
8. Add Cheese: Sprinkle shredded mozzarella cheese on top of the meatballs in each roll.
9. Bake Again: Return the assembled sandwiches to the oven and bake for an additional 10 minutes, or until the cheese is melted and bubbly.
10. Serve: Remove from the oven and let them cool for a minute before serving.

These simple steps will guide you in creating incredible Meatball Sub Sandwiches that are sure to delight everyone at the table!