Preheat your oven to 425°. Coat a glass or ceramic baking dish in olive oil. Add 1 portobello cap per person. Top with your favorite protein and veggie combo. Bake until everything is soft and the liquid in the dish begins to evaporate.
In this photo, my mushrooms are topped with pre-cooked zucchini, peppers, cabbage, carrots, garbanzo beans, garlic, herbs, S&P, and Daiya shreds.
If heirloom tomatoes are tolerable, add a slice seasoned with garlic and italian herbs and some Daiya to make a low carb entree. Grilled eggplant slices work well with mushrooms too. Mushrooms are versatile work well with other veggies. Experiment with some flavor profiles, different sauces and seasonings and see how it goes. :D