Preheat oven to 350°F and grease a 9x13" pan with cooking spray.
Remove slider buns from their package and slice horizontally, so you have a top layer and a bottom layer.
Place the bottom layer into the prepared pan.
Arrange five slices of cheese in an even layer.
Next, add 12 meatballs in four rows of three. (You want the meatballs to be hot, so make sure they're cooked before you place them on the cheese)
Spread about 2 tsp pizza sauce over each meatball.
Arrange remaining cheese slices over the meatballs.
Top the sliders with the bun tops and set aside.
Make the sauce by combining the melted butter, parmesan, garlic and parsley; brush it over the sliders.
Cover the sliders with foil and bake for 25 minutes, or until the cheese is all melted.
Serve warm and enjoy!