Preheat your oven to 400 degrees F (200 degrees C).
In a large bowl add the Chicken Breast (1), Pizza Sauce (3/4 cup) and Shredded Parmesan Cheese (1/4 cup). Mix together.
Place your Portobello Mushroom (1) on a large parchment paper-lined baking tray. Remove the core and using a spoon scrape out the gills.
Pour in the chicken mixture and sprinkle Shredded Mozzarella Cheese (to taste) over the top.
Place in your preheated oven and bake for about 17 minutes. Once the mushroom is cooked and cheese is melted, remove and serve.