Preheat oven to 400 degrees.
Fry and crumble bacon. Wilt spinach leaves in olive oil for 2-3 minutes in frying pan.
Clean your portabella mushrooms and remove stems.
Put wilted spinach and bacon in upside-down mushroom cap, with mozzarella cheese on top. Put portabellas on baking sheet.
Cook the portabella pizzas in the oven for 10-12 minutes and enjoy!
Variations: Feel free to add whatever vegetables you want to this pizza. You can also make them in smaller mushrooms to serve as appetizers.