Remove stems from mushrooms and scrape the gills (the black underside). Drizzle with olive oil and place on a lined baking sheet. Bake for about 7 minutes. Drain liquid off of mushrooms and pat dry with clean paper towels. Spread underside of mushrooms with pizza sauce, then sprinkle with 1/2 of the cheese. Top with pepperoni and black olives and remaining cheese. Bake for an additional 7 to 10 minutes or until cheese is well melted.