Preheat your oven to 375°F (190°C).
In a large bowl, combine the ground turkey, bread crumbs, Parmesan cheese, parsley, milk, onion, garlic, oregano, salt, and black pepper. Mix well.
Shape the mixture into small meatballs, about 1 inch in diameter.
Place the meatballs on a baking sheet lined with parchment paper. Bake for 20 minutes or until cooked through.
While the meatballs are baking, slice the slider buns in half and place them on another baking sheet.
After the meatballs are cooked, remove them from the oven and top each one with a slice of mozzarella cheese. Return them to the oven for a few minutes, until the cheese is melted and bubbly.
Spread marinara sauce on the bottom half of each slider bun. Top with a meatball and a few slices of pepperoncini peppers.
Garnish with fresh basil leaves, if desired.
Place the top half of the slider bun on each meatball and serve.