Prepare the Meatballs:

1. Mix the Ingredients: In a large bowl, combine the ground beef or turkey, egg, breadcrumbs, Parmesan cheese, garlic, parsley, onion powder, oregano, salt, and pepper. Mix gently until just combined; avoid overmixing to keep the meatballs tender.
2. Shape the Meatballs: Roll the mixture into small, uniform meatballs (about 1 inch in diameter) and place them on a baking sheet lined with parchment paper.
3. Cook the Meatballs: Preheat your oven to 375°F (190°C). Bake the meatballs for 15-18 minutes, or until cooked through (internal temperature of 165°F/74°C). Alternatively, you can pan-fry them in a skillet over medium heat until browned and cooked through.

Assemble the Sliders:

4. Prepare the Buns: Slice the slider buns in half. Arrange the bottom halves on a baking sheet or in a large baking dish.
5. Add the Meatballs: Place one meatball on each bun bottom. Top each meatball with a spoonful of marinara sauce and half a slice of mozzarella or provolone cheese.
6. Top with Buns: Place the top halves of the buns over the cheese.

Bake the Sliders:

7. Prepare the Butter Topping: In a small bowl, mix the melted butter with garlic powder and Italian seasoning. Brush the butter mixture over the tops of the buns.
8. Bake: Preheat your oven to 350°F (175°C). Bake the sliders for 10-12 minutes, or until the cheese is melted and the buns are lightly golden.

Serve and Garnish:

9. Garnish and Serve: Remove the sliders from the oven and garnish with fresh basil leaves and grated Parmesan cheese, if desired. Serve warm and enjoy!