Preheat oven to 400°F. Brush both sides of mushroom caps with olive oil.
Place on a baking sheet and bake 13–15 minutes. Dab dry with paper towels.
Spread pizza sauce onto each mushroom.
Add bell pepper, onion, mozzarella, and tomatoes.
Switch oven to broil. Broil 3–5 minutes, watching closely, until cheese is browned and bubbly.
Remove from oven, sprinkle with basil, parsley, and optional truffle salt and pepper. Serve immediately.
See full steps with tips & photos → https://theboatshedcafe.com/portobello-pizza/