Heat the oven to 400 degrees. In a mixing bowl, stir together the ground beef, breadcrumbs, egg, garlic, oregano, salt, and pepper until evenly combined.
Shape the mixture into 8 meatballs of equal size and place them on a baking sheet.
Bake the meatballs for 18 minutes until they reach an internal temperature of 160 degrees.
While the meatballs cook, warm the marinara sauce in a skillet over medium heat.
Add the baked meatballs to the skillet and turn them to coat in the sauce.
Split the slider buns and place two meatballs on each bottom half. Spoon extra sauce over the meatballs.
Sprinkle mozzarella cheese on top and broil for 1 to 2 minutes until the cheese melts. Add the bun tops and serve.