Score the middle of each chicken breasts. Season with salt and pepper.
Heat a well-oiled skillet over medium-high heat. Sear the chicken breasts for 5 minutes per side. Reduce the heat to medium-low and cover the chicken breasts. Cook for an additional 10 minutes or until cooked throughout. To prevent dark charring, add a ¼ cup water to the skillet before covering with a lid.
While the chicken is cooking, combine the hot cooked mashed potatoes with butter, cream cheese and cooked bacon pieces.
Place the chicken on a lined baking pan with parchment. Spoon the potato mixture into the slit on the top of each chicken breasts. Divide the cheddar cheese on top of each potato-filled chicken breast. Heat in the oven for 7-10 minutes.
Finish the chicken with the green onions and sour cream.