Using a damp paper towel, wipe off the mushroom caps. Remove the stems and scrape the gills with a spoon.
Cover a baking sheet with aluminum foil, place the mushroom caps gill side down onto the baking sheet and pre-bake for about 8 minutes.
Transfer the mushroom caps onto a dry paper towel to remove any moisture.
Place the mushroom caps back on the baking sheet and brush with 1 tablespoon olive oil.
Add 1 tablespoon pizza sauce to the inside of each cap.
Fill the caps with mozzarella cheese, pepperoni bits, and any other desired toppings.
Sprinkle the top with Parmesan cheese.
Bake at 375 degrees for 15-20 minutes or until the cheese is melted.
Notes
Assorted toppings such as black olives, sliced cherry tomatoes, sauteed garlic, onions and peppers, spinach, etc. can be added according to your tastes.