Combine the cheese soup and milk and whisk until smooth. Put aside 1 cup to use later.
Wash and peel the potatoes then cut into thin slices (about 1/4 inch thick). Thinly slice the onion as well.
Spray the sides and bottom of a 13x9 baking dish with cooking spray. Spoon 1/4 of the cheese soup mixture Into the bottom of the dish. Add a single layer of the potato slices and onion and season with salt and pepper. Spoon another 1/4 of the soup mixture over potatoes. Repeat this process two more times so you have three layers of potatoes and onions topped with soup mixture seasoning with salt and pepper each time. Cover the dish tightly with foil and bake at 350 degrees for 30 minutes.
Cook bacon until browned and crispy and set aside.
Season the chicken tenderloins with salt and pepper then sauté in the bacon drippings over medium high heat until lightly browned. This is not to cook the chicken through, but to sear the sides. Set aside.
Remove dish from the oven and uncover. Arrange chicken tenderloins on top of the potatoes and pour the reserve soup mix over the chicken. Cover lightly again and continue cooking for 30 minutes.
Remove the dish from the oven and uncover. Sprinkle shredded cheese evenly over the chicken and potatoes then top with bacon pieces. Return dish to the oven and continue cooking, uncovered for 5 - 10 minutes or until cheese is melted and bubbly.