Place the roast into a crockpot on low heat. Pour beef stock and Worcestershire over the roast and sprinkle Montreal steak seasoning on the top surface of the roast.
Cook for 6-8 hours.
Remove roast from the crockpot and shred into large chunks with two forks, removing any fat. Place the shredded beef back into the crockpot with the drippings so that it will stay moist.
Sauté green peppers and onions in butter over medium heat for about 5 minutes until they begin to soften. Season with salt and pepper.
To build the sandwiches, slice the rolls in half and butter each side. Place shredded beef, cheese, onions and peppers on one side of the roll. Place the sandwiches on a baking sheet open faced to melt the cheese and toast the rolls.
Turn oven to broil, and watch closely for the cheese to melt and the bun to toast.