Do the prep. Preheat the oven to 350°F or 177°C. Halve the dinner rolls, set the lower halves on a baking sheet, and set aside.
Make the meatballs. In a large bowl, combine the ground beef, egg, salt, pepper, garlic powder, Parmesan and 2 tablespoons chopped basil. Mix the ingredients until well combined. Form 12 golf-ball sized-meatballs and set them aside.
Fry the meatballs. Heat oil in a large skillet over medium-high heat. Add the meatballs and cook for 1-2 minutes per side, then flip. They will finish cooking in the next step. Remove the meatballs to a plate lined with paper towels. Drain any excess grease from the pan.
Finish the meatballs. Pour the marinara sauce into the pan and place the meatballs into the sauce. Cook for 8-10 minutes, flipping occasionally until the sauce has reduced to a thick consistency. Remove from heat.
Assemble the sliders. Place one meatball atop each halved dinner roll. Top with sliced mozzarella and cover with the top roll.
Make the garlic butter. In a small bowl combine the melted butter, garlic, basil, and Parmesan. Mix well. Pour the garlic butter over the top of the sliders.
Bake. Place into the oven and bake for 15-20 minutes, until the rolls are golden brown and the cheese has melted.