Slice the French bread in half lengthwise. Place both halves cut-side up on a parchment-lined baking sheet.
Using a small microwaveable bowl, melt butter. Add garlic, Parmesan cheese and Italian seasonings; stir until well combined. Spread this mixture evenly over the tops of both halves of bread.
Next, sprinkle mozzarella evenly over both halves of bread.
Using a large bowl, add marinara sauce and cooked/halved meatballs; toss until well coated. Using a slotted spoon, place meatballs on top of bread. Sprinkle sliced red onions and fresh basil on top.
Bake for 10-12 minutes, or until cheese has fully melted.
Garnish with additional grated Parmesan cheese before slicing and serving.