Heat the oven to 350°F. Cook mushrooms in oil over medium-high heat for 7 to 8 minutes until browned and dry.
Split the connected Hawaiian rolls horizontally and place the bottoms in a parchment-lined 9-by-13-inch pan. Spread pizza sauce over the bread, leaving a small border.
Layer on half the mozzarella, mushrooms, pepperoni and remaining mozzarella. Replace the top slab.
Mix butter with oregano and garlic powder, brush over the tops and cover with foil. Bake for 15 minutes, then uncover for 8 to 10 minutes until the cheese melts and the center reaches 165°F.
Rest for 5 minutes and cut into 12 sliders.