Preheat the oven to 400°F (200°C). In a mixing bowl, combine ground beef, breadcrumbs, Parmesan cheese, egg, garlic, oregano, salt, and pepper. Mix until just combined.

Form the mixture into meatballs, about 1 inch in diameter, and place them on a baking sheet.

Bake in the preheated oven for 20 minutes or until cooked through.

While the meatballs are baking, heat marinara sauce in a skillet over medium heat.

Once the meatballs are done, add them to the skillet with the marinara sauce and simmer for 5 minutes.

To assemble, place meatballs and sauce into toasted sub rolls, top with mozzarella cheese, and return to the oven for 5 minutes until cheese is melted.

Garnish with fresh basil before serving.