Prepare meatballs as per instructions. If using store-bought, add sauce and meatballs to a pan and heat for 10 minutes.
Preheat the oven to 350 degrees F.
Cut slider buns so you have tops and bottoms.
Place bottoms in a 9x13 inch baking dish
Place 6 slices of mozzarella cheese down on the slider buns, covering them.
Add a dab of marinara sauce on each slider bun bottom
Add a meatball to each slider bun bottom
Add a dab of marinara sauce on top of the meatball
Add remaining 6 slices of mozzarella cheese, covering all the meatballs
Place tops of slider buns on top
Melt the butter and add the Italian seasoning to it
Brush the butter mixture over the tops of the slider buns
Top buns with parmesan cheese (optional)
Cover with aluminum foil and bake for 10-12 minutes
Remove aluminum foil and bake for an additional 5-7 minutes until buns are golden and cheese is melting
Remove from oven and allow to rest for 5 minutes
Serve and enjoy!