Preheat your oven to 350°F (175°C). Prepare your baking dish by lightly greasing it or lining it with parchment paper.
Carefully slice the package of Hawaiian sweet rolls in half horizontally, keeping the rolls connected.
Place the bottom half of the rolls in the prepared baking dish. Spread half of the pizza sauce evenly over the rolls.
Sprinkle 1 1/2 cups of shredded mozzarella cheese over the sauce, then layer the mini pepperoni across the cheese.
Spread the remaining pizza sauce over the pepperoni and top with the remaining mozzarella cheese. Place the top half of the rolls over the cheese.
In a mixing bowl, combine the melted butter, dried minced onion, Parmesan cheese, dried oregano, garlic powder, kosher salt, and black pepper. Mix well.
Generously spread the butter mixture over the top of the rolls.
Cover the baking dish with aluminum foil and bake for 15 minutes. Remove the foil and bake for an additional 10-15 minutes, or until the cheese is bubbly and tops are golden brown.
Let the sliders cool for a few minutes, then garnish with parsley and additional Parmesan cheese if desired. Slice and serve warm with extra pizza sauce on the side.