First, make the meatball mixture. Combine beef, bread crumbs, parmesan cheese, parsley, basil, oregano, salt, pepper, garlic, and egg in a large bowl. Mix with hands or spoon until meatball mixture has formed.
Portion out your meatballs with hands or cookie scoop, then roll in hands to form meatballs. Continue with remaining mixture. You should get 18-21 meatballs.
Heat a non-stick large skillet to medium heat. Add a little olive oil and heat over medium-high heat. Add meatballs and brown on all sides, about 1-2 minutes per side until a light golden brown color begins to form.
Remove from heat, pour sauce over meatballs, then top with mozzarella cheese. Cover the skillet, and return to the burner over medium-low heat.
Allow to simmer for 10-15 minutes, or until the meatballs are cooked through and the cheese has melted. Garnish with optional herbs.
Assemble the sliders. Place two meatballs on each bottom bun, making sure that marinara sauce and cheese is scooped up along with each meatball.
Add the top buns
Prepare the garlic butter. Melt butter in a small bowl, Add garlic, salt and parsley flakes. Brush garlic butter on top of the sliders with a pastry brush.
Serve warm.
Notes
If you don't want to finish your meatballs on the stovetop, you can bake them! Transfer the seared meatballs to a baking dish or rimmed sheet pan before you top each meatball with sauce and cheese, then bake for about 15 minutes at 375 degrees Fahrenheit.