Portobello mushroom Pizza! Delicious Clean eating! After you clean the mushroom caps, bake them in the oven at 400 degrees for 10 minutes. Then remove from oven and apply pizza sauce and toppings. Bake for another 10 minutes or until cheese is melted and browning. (If you use more mozzarella.) Paleo, Gluten Free, Vegetarian, Low-carb, Low-Cal and Low-Fat! AND Super easy to make!