Preheat the oven to 375°F (190°C).
In a large bowl, combine ground beef, breadcrumbs, grated Parmesan cheese, egg, 2 cloves minced garlic, chopped fresh parsley, salt, black pepper, dried oregano, and dried basil. Mix until all ingredients are evenly incorporated.
Shape the mixture into 12 evenly sized meatballs and place them on a baking sheet lined with parchment paper.
Bake the meatballs in the preheated oven for 15-20 minutes, or until cooked through and browned on the outside.
While the meatballs are baking, cut the French bread loaf in half lengthwise.
In a small bowl, mix the softened butter, 3 cloves minced garlic, chopped fresh parsley, and salt until well combined.
Spread the garlic butter mixture evenly over the cut sides of the bread halves.
Once the meatballs are cooked, remove them from the oven and spoon marinara sauce evenly over each meatball.
Place the meatballs with sauce on one half of the garlic buttered bread.
Sprinkle shredded mozzarella cheese over the meatballs and sauce.
Place the other half of the bread on top to create a sandwich.
Wrap the garlic bread meatball sandwich in aluminum foil and bake in the oven for an additional 5-7 minutes, or until the cheese is melted and the bread is toasted.
Remove from the oven, unwrap, slice into portions, and serve warm.