Preheat the oven to 375°F (190°C) and line a baking sheet with parchment paper.
Season ground beef with salt and black pepper, then form into 12 small patties; cook in a skillet over medium heat for 3-4 minutes per side until browned, then set aside.
Slice slider buns in half, place a patty on each bottom half, and top with shredded cheddar cheese; place the top halves on the baking sheet beside them.
Mix melted butter with minced garlic, grated Parmesan, and chopped parsley, then brush generously over the tops of the buns.
Bake for 8-10 minutes until the cheese is melted and the buns are golden and glossy.
Assemble by placing the cheesy patties between the buns and serve warm.