I marinated them in a little balsamic vinegar, and low-fat italian dressing for 10-15 minutes before I cooked them, just to give them a little more flavor. No real recipe, just tossed a bunch of things together that I had on hand. This was a good South Beach recipe, to boot and very filling.
Portobello mushroom caps, cleaned and stems removed
Red bell pepper, chopped
spinach (I had frozen)
artichoke hearts, chopped
Preheat oven to 400 degrees. After marinating the mushrooms, heat a pan over medium-high heat. Spray with cooking spray, add mushroom caps (marinade and all; gill side up) cook for a minute or two, until it starts to get tender. Flip and cook another minute or so. Remove to a baking dish, sprayed with cooking spray, gill side up. Add all of the veggies to the pan and sautee until spinach is thawed and liquid has cooked off. Divide filling between the mushroom caps. Top with cheese. Bake for 10-15 minutes until cheese is melted and mushrooms are cooked thru.