Add meatballs to the sauce. Cover, and allow to simmer for a minimum of 10 minutes in the sauce.
Cut the baguettes in half and divide the fresh mozzarella evenly between the three. Toast until the cheese has melted.
Place each toasted bread with cheese on a plate, slather each with pesto and top with warmed meatballs and sauce. Sprinkle with grated parmesan and serve immediately.
Recipe by Slice of Jess at https://sliceofjess.com/super-cheesy-meatball-sandwich/