Preheat oven to 350 degrees F.

Spray a 9 x 13 inch baking pan with cooking spray.

In a small bowl mix together melted butter, garlic powder, onion powder and Italian seasoning and set aside.

Slice rolls through the middle of the buns so there is a top and bottom half. Place bottom half in prepared baking pan. Top with 6 slices of mozzarella cheese. Top with half of the pepperoni slices and all the onion slices. Repeat with remaining cheese and pepperoni. Top with remaining half of rolls.

Brush tops of rolls with melted butter mixture. Top with shredded mozzarella and grated Parmesan cheeses.

Cover with foil and bake in preheated 350 degree oven for 10 - 15 minutes until cheese on top is melted and rolls are heated through. Remove from oven and slice rolls into slider portions along roll guides.

Serve with additional pizza sauce for dipping, if desired.