Remove the chicken meat from the bones and tear into bite-size pieces. Mix the chicken with the balsamic vinaigrette dressing and mustard. Season with salt and pepper. Preheat the broiler. Brush mushrooms with butter and place under broiler for 5 minutes. Turn them, and cover with the Swiss cheese. Return to the broiler for an additional 2 minutes or until the cheese is lightly browned. Spread the bottom of the loaf with the Newfchatel cheese. In order, layer chicken, tomato slices, Jack cheese and Swiss-covered mushrooms. Cover with top of loaf.