Prepare the Meatballs:

1. Mix the Meatball Ingredients: In a large mixing bowl, combine the ground beef, ground chicken or lamb, breadcrumbs, Parmesan cheese, minced garlic, chopped parsley, onion powder, garlic powder, Italian seasoning, egg, milk, and a pinch of salt and pepper. Mix the ingredients together with your hands or a spoon until everything is well incorporated. Be careful not to overmix, as this can make the meatballs tough.
2. Form the Meatballs: Using your hands, form the mixture into small meatballs, about 1 1/2 inches in diameter. You should have around 18-20 meatballs.
3. Cook the Meatballs: Heat a large skillet or frying pan over medium heat and add a splash of olive oil. Once the oil is hot, add the meatballs to the pan in batches. Cook for about 3-4 minutes per side, until the meatballs are browned on the outside. You may need to turn them a few times to ensure even cooking. Once browned, reduce the heat to low and let the meatballs cook through, about 10 minutes. Alternatively, you can bake the meatballs at 375°F (190°C) for 15-20 minutes if you prefer a hands-off method.

Prepare the Sliders:

4. Preheat the Oven: While the meatballs are cooking, preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper for easy cleanup.
5. Slice the Rolls: Carefully slice the King’s Hawaiian rolls in half horizontally, keeping them intact as a whole (so you have a top and bottom half of the slider bun). Place the bottom halves on the prepared baking sheet.
6. Assemble the Sliders: Once the meatballs are cooked, arrange them evenly over the bottom half of the rolls. Spoon a little marinara sauce on top of each meatball, then place a slice of mozzarella cheese over the sauce. Add a few more meatballs if needed to fill out the sliders.
7. Add the Top of the Rolls: Place the top half of the rolls over the meatballs, gently pressing down to compact them slightly. If you like, brush the top of the rolls with a bit of melted butter for an extra touch of flavor and golden color.
8. Bake the Sliders: Bake the assembled sliders in the preheated oven for 10-12 minutes, or until the cheese is melted and the top of the rolls is golden brown.

Serve the Meatball Sliders:

9. Garnish and Serve: Once the sliders are done baking, remove them from the oven and let them cool for a few minutes before slicing them into individual sliders. Garnish with fresh basil or parsley, if desired. Serve immediately while warm and enjoy!