Per Eating Well, "Portobello caps make excellent mini casseroles. Here, they hold a tomato, cheese and olive stuffing that grills up to a smoky perfection. Serve them with whole-wheat couscous and a mixed green salad for an easy meal." This is a low calorie, vegetarian main dish. NOTE: after having made this delicious dish, I have made a couple changes to the original recipe. I served mine atop spinach.