Preheat the oven to 350°F (175°C). Lightly season both sides of the 4 chicken breasts with 1 teaspoon of the lemon pepper.
Place the seasoned chicken breasts in a baking dish and bake for 20 minutes.
While the chicken bakes, whisk together the cream of chicken soup, shredded cheddar, mayonnaise, milk, the remaining 1 teaspoon lemon pepper, and chopped parsley (if using) in a mixing bowl until smooth.
Remove the partially baked chicken from the oven and pour the soup mixture evenly over the breasts.
Return the dish to the oven and bake an additional 20–40 minutes, until the internal temperature of the chicken reaches 160°F (71°C) and the juices run clear.
Let the chicken rest for 10 minutes to allow the sauce to thicken before serving.