I had some portabello mushrooms to use before they went bad and I looked online for a stuffed mushroom recipe and I found http://whatscooking.us/2008/03/05/lunch-special-stuffed-creamy-portabella-mushrooms/
Which looked delicious so I decided to modify the recipe to make it vegetarian and made out of stuff I had on hand. I was extremely happy with the result so I'm going to share.
Step 1) put a stick of butter, 6 0z of cream cheese 1/4 cup water, 1 tablespoon sugar, and 1 tablespoon grapefruit juice in a sauce pan and heat and stir until it thickens a bit.
Step 2) Add a diced red bell pepper, garlic powder and chili powder to taste to the sauce and let simmer
Step 3) Dice and Sautee an onion in a separate pan. Remove the stems from your portabell0 mushrooms chop them up and add them to the onion and let them cook for a bit.
Step 4) Add the onion and mushrooms to the cream sauce and fill the mushrooms with the mixture.
Step 5) Top the mushrooms with parmesan cheese and bread crumbs.
Step 6) Broil the mushrooms until the bread crumbs are a golden brown.
I was making 4 stuffed portabello's with the above recipe and I had a bit too much sauce but some of my mushrooms were much smaller than the others so your milage may vary.