Although this can be assembled and cooked the day you plan to serve it, the flavors meld better if prepared, covered and refrigerated 1 - 2 days in advance.
Wrap each breast with a strip of bacon and secure with toothpicks. (For smaller servings cut breasts and bacon strips in half lengthwise, then wrap w/ cut bacon - depending on how hearty the eaters, this will make more servings)
Spread halved chipped beef slices evenly over bottom of a 9x13 inch baking dish. Top with wrapped chicken.
Mix soup (+ mushrooms if using cream of mushroom soup) and sour cream and pour over chicken.
Preheat oven to 275 degrees. Place dish in oven uncovered and cook for 3 hours.