This is very simple to make:
1lb Deli roast beef - I buy it from the Deli counter so its not prepackaged roast beef
I jar of Kraft Double cheddar cheese - you can find this with the speghetti sauces
1 Lg Onion
1 Package of fresh mushrooms, or canned if you don't have fresh
1 package of rolls of your choice - I love the sara lee onion rolls
Cut onion into strips, not diced, and slice mushrooms, saute' onion till soft and add mushrooms and cook till soft as well, when they are warmed through add your jar of cheddar sauce, warm through and set aside. In a pan take slices of the roast beef and heat them through, place on roll and add your onion, mushroom, cheese mixture on top.