In a large mixing bowl, combine ground beef, breadcrumbs, egg, Parmesan, garlic, oregano, basil, salt, pepper, and parsley. Mix gently—overmixing can make the meatballs tough.

Roll into 1 to 1½-inch meatballs and place them on a parchment-lined baking sheet.

Bake at 400°F (200°C) for 18–20 minutes until browned and cooked through. Baking keeps cleanup easy and helps the meatballs retain their shape.

Transfer the cooked meatballs to a skillet or Dutch oven. Add marinara sauce and simmer for 5–7 minutes so the flavors blend and the meatballs absorb extra sauce.

Slice the sub rolls lengthwise without cutting all the way through. Brush lightly with olive oil and toast in the oven for 2–3 minutes until warm and crisp.

Spoon several meatballs and plenty of sauce into each roll. Add mozzarella and Parmesan on top.

Place the subs under the broiler for 1–2 minutes until the cheese melts and starts to bubble lightly. Keep a close eye to avoid over-browning.

Garnish with fresh basil or extra Parmesan. Serve warm with chips, salad, or roasted vegetables.