01 - Preheat oven to 400°F (200°C).
02 - In a large bowl, combine ground beef, breadcrumbs, Parmesan cheese, egg, minced garlic, parsley, oregano, salt, and pepper. Mix gently until just combined—avoid overworking the meat.
03 - Form the mixture into 12 equal-sized meatballs, approximately the size of a golf ball.
04 - Heat a large skillet over medium heat with a splash of oil. Brown the meatballs on all sides for 5–7 minutes until evenly seared.
05 - Pour marinara sauce over the meatballs in the skillet. Simmer gently for 10–15 minutes, turning occasionally, until the meatballs are fully cooked through.
06 - Combine softened butter with minced garlic. Slice the sub rolls open and lightly spread with the garlic butter mixture. Place on a baking sheet and toast in the oven for 2–3 minutes until lightly golden.
07 - Place 3 meatballs along with a generous spoonful of sauce into each toasted roll. Top evenly with shredded mozzarella cheese.
08 - Return the assembled subs to the oven and bake for 5–7 minutes, until the mozzarella is fully melted and bubbly.
09 - Serve hot, garnished with additional chopped parsley or grated Parmesan if desired.