Creating Cheesy Meatball Subs is straightforward with these simple steps:

1. Preheat your Oven: Set your oven to 375°F (190°C).
2. Mix Meatball Ingredients: In a large bowl, combine the ground beef, breadcrumbs, Parmesan cheese, chopped parsley, egg, minced garlic, salt, black pepper, and Italian seasoning. Mix until just combined.
3. Shape Meatballs: Form the mixture into meatballs, about 1 inch in diameter. Place them on a baking sheet lined with parchment paper.
4. Bake Meatballs: Bake the meatballs in the preheated oven for 20-25 minutes, or until they are cooked through.
5. Heat Marinara Sauce: While the meatballs are baking, heat the marinara sauce in a saucepan over medium heat until warm.
6. Prepare Sub Rolls: Cut the sub rolls in half lengthwise, but not all the way through, creating a pocket for the meatballs.
7. Assemble the Subs: Once the meatballs are done, place several meatballs into each sub roll. Spoon marinara sauce over the meatballs generously.
8. Add Cheese: Top each sub with a generous amount of shredded mozzarella cheese.
9. Melt Cheese: Place the assembled subs back in the oven for an additional 5-10 minutes, until the cheese is melted and bubbly.
10. Garnish and Serve: Remove from the oven, garnish with extra parsley if desired, and serve hot.

By following these steps, you can create cheesy meatball subs that are not only delicious but also visually appealing.