Always remove the stems from portobello mushrooms, as they are too woody to eat. Portobello stems can be saved and added to soup stock.
To broil mushroom caps, place on broiler pan; broil 4 to 6 inches from heat using times above as a guide, turning once. Meanwhile, brush cut sides of rolls with 1/4 cup salad dressing. During last 1 to 2 minutes of cooking time, place cheese on mushrooms and place buns, cut side up, on broiler pan to toast.