Preheat oven to 350°F. Line a 9x13 baking dish with parchment paper or foil.
Using a large serrated knife, slice the entire slab of rolls horizontally, keeping the rolls connected. You'll have one connected top portion and one connected bottom portion.
Place the bottom slab of rolls in the baking dish.
Begin layering by spreading 1 cup mozzarella cheese evenly across the bottom rolls. Next, place one cooked meatball on each roll section. Spoon marinara sauce evenly over all the meatballs, then finish by covering everything with the remaining mozzarella cheese.
In a small bowl, combine melted butter, garlic powder, Italian seasoning, and Parmesan cheese.
Place the top slab of rolls on top of the meatballs and cheese. Brush the butter mixture evenly over the top of the rolls.
Bake uncovered for 7-10 minutes, or until cheese is melted and tops are golden brown.
Let rest for 2-3 minutes before serving. Use a serrated knife to cut into individual sliders.