Heat oven to 375 degrees F. Place marinara sauce in large saucepan. Set sauce over medium heat until it begins to bubble. Add in frozen meatballs and stir until their coated in sauce. Let them cook until no longer frozen and are heated through, about 20-25 minutes.

In the meantime, prepare the rest of the ingredients. Slice each bun and place in a 13x9 baking dish. Set aside until meatballs are ready. Stack slices of provolone on top of each other. Slice evenly in half. Set aside.

When meatballs are ready, turn off heat. Using a spoon, scoop four meatballs from marinara and place into one hot dog bun. Repeat with 6 remaining buns. Spoon a little sauce over each sub, covering meatballs in sauce.

Sprinkle a little Parmesan cheese evenly over each sub. Place one half-slice of provolone cheese on the sub, covering the top half. Place another half-slice on the same sub, but now covering the bottom half. The meatballs should be completely covered in cheese. Sprinkle with a little bit of Italian seasoning (or oregano). Repeat with other subs.

Place subs in preheated oven and bake for 8 minutes, or until cheese is completely melted. Remove from oven and let cool for 5 minutes before serving.