After a bit of experimenting, I came up with my version of a portabella cheese steak. Brushing the mushroom caps with the marinade before you slice them, allows them to soak up the flavor, but not a lot of liquid.
Mix together "beef" broth, olive oil, worcestershire sauce and garlic. Brush both sides of the portabella mushrooms with marinade, you will have some left, save it, you will use it for cooking the peppers and onion. Allow mushrooms to set about 30 minutes.
Toast the buns. (Brush inside of buns with a little olive oil and place under the broiler until toasted) Set aside.
Slice mushrooms in 1/2 inch wide strips .
Place pepper and onion and the rest of the marinade in a large skillet. Cover and cook over medium heat, about 5-6 minutes, until just tender, stirring occasionally.
Add mushrooms, salt and pepper, cover and cook for about 5 more minutes, until mushrooms are done, stirring once or twice.
Slather buns with Hellmann's mayonnaise - or your favorite brand. On the bottom half of the buns, divide the mushroom mixture between them.
Top with 1 or 2 slices of your favorite cheese. Place under the broiler until melted. Serve.