In a large mixing bowl, combine the ground beef, breadcrumbs, grated Parmesan cheese, egg, minced garlic, finely chopped onion, dried oregano, salt, and black pepper. Mix until all ingredients are well combined.

Form Meatballs

Shape the mixture into meatballs, about 1 inch in diameter, and place them on a baking sheet lined with parchment paper.

Bake Meatballs

Bake the meatballs in the preheated oven for 20-25 minutes, or until they are cooked through and browned on the outside.

Sub Assembly

Prepare Marinara Sauce

While the meatballs are baking, heat the marinara sauce in a saucepan over medium heat until it is warmed through.

Assemble Subs

Once the meatballs are done, remove them from the oven. Place 3-4 meatballs in each sub roll and spoon marinara sauce over the top.

Add Cheese and Basil

Sprinkle shredded mozzarella cheese over the meatballs and add chopped fresh basil.

Melt Cheese

Place the assembled subs back in the oven for an additional 5-7 minutes, or until the cheese is melted and bubbly.

Serve

Remove from the oven and serve hot, garnished with additional basil if desired.