Step 1

Preheat oven to 400 degrees F.

Step 2

Place mushrooms on a rimmed baking sheet. Stir pizza sauce and Italian seasoning together in a small bowl. Spread 2 tablespoons of the sauce over the inside of each cap. Sprinkle with bell pepper and onion, then cheese. Top with pepperoni.

Step 3

Bake until the mushrooms are hot and the cheese is melted, about 15 minutes.