Take first 5 ingredients and place in pot roast early in the day and cook in Crock Pot all day.
Shortly before ready to eat sauté your onions in a little butter and some of the sauce that the pot roast cooked in.
While that is going, take the roast out of pot and shred it, which you can also do before the onions.
To serve place some shredded meat on your roll, a little mayonnaise, onions and cheese and microwave just to melt cheese.