Place bell pepper, onion, mushrooms and roast in slow cooker.
Mix Seasoning Mix and water until well blended. Pour over roast and vegetables. Cover.
Cook 8 hours on LOW or 4 hours on HIGH. Remove roast and vegetables from slow cooker. Skim fat from au jus.
Slice beef into thin slices. Return beef to slow cooker. Place beef and vegetables on rolls. Top with cheese. Broil 2 minutes or until cheese is melted. Serve sandwiches with au jus on the side for dipping.