Preheat oven to 400 F. In a large bowl, combine ground beef, breadcrumbs, grated parmesan cheese, Italian seasoning, milk and egg. Mix together until combined.
Roll meatballs into small balls and place onto a large greased baking sheet. Bake for 20-25 minutes.
Open sub buns and place onto a baking sheet. Spread bread lightly with olive oil. Bake for 5-7 minutes. Place 3-4 meatballs on each sub bun.
For the marinara sauce, in a medium bowl combine crushed tomatoes with Italian seasoning. Pour the sauce evenly over the meatballs. Top each sandwich with shredded mozzarella cheese.
Bake for 2-3 minutes, until the cheese has melted.
