A perfect low-calorie alternative for when you have the craving for pizza!
Place the mushroom cap upside down on a cookie sheet. Spread the marinara sauce over the mushroom, and top with bell pepper, onion, and cheese - just like a normal pizza.
Bake in 350°F oven until the cheese melts and the "pizza" is warmed through.
Try experimenting with different vegetables or cheeses. (Suggestions are not included in the nutritional analysis.)