01 - Preheat oven to 400°F and line a baking tray with parchment paper.
02 - In a large mixing bowl, combine ground beef, breadcrumbs, Parmesan cheese, egg, garlic, parsley, oregano, salt, and black pepper. Mix gently until just combined.
03 - Form mixture into 12 evenly sized meatballs. Arrange on the prepared baking tray.
04 - Bake in the oven for 15 to 18 minutes, or until meatballs are cooked through and browned.
05 - While meatballs bake, heat marinara sauce in a small saucepan over low heat until hot.
06 - Slice slider buns and place the bottom halves on a separate baking sheet.
07 - Place one meatball on each bun bottom. Spoon warm marinara sauce over each meatball and top with a slice of mozzarella cheese.
08 - Add two black olive slices to each slider to create 'eyeballs' atop the melted cheese.
09 - Arrange bun tops nearby. Brush each with melted butter and sprinkle with garlic powder.
10 - Bake assembled sliders open-faced for 5 to 7 minutes, or until cheese melts and buns are lightly toasted.
11 - Place bun tops on sliders. Garnish with chopped fresh basil or parsley and serve warm.