Preheat your oven to 400°F (200°C).
In a large bowl, combine ground beef, breadcrumbs, Parmesan, parsley, egg, garlic, Italian seasoning, salt, and pepper.
Mix well until all ingredients are combined.
Form the mixture into small meatballs, about 1 inch in diameter.
Place meatballs on a baking sheet lined with parchment paper.
Bake for 20 minutes until cooked through.
While meatballs are baking, heat marinara sauce in a small saucepan.
Slice slider buns in half and toast lightly in the oven.
Assemble sliders: place a meatball on the bottom half, spoon marinara sauce over it, and add mozzarella cheese.
Top with the other half of the bun and serve warm.