Preheat the oven to 350°F (175°C). Lightly season the 4 chicken breasts with 1 teaspoon of the lemon pepper and place them in a baking dish.
Bake the chicken for 20 minutes until partially cooked.
While the chicken bakes, whisk together the cream of chicken soup, shredded cheddar, mayonnaise, milk, the remaining 1 teaspoon lemon pepper, and optional parsley in a bowl until smooth.
Pour the sauce evenly over the partially baked chicken.
Return the dish to the oven and bake an additional 20–40 minutes, depending on breast size, until the chicken reaches 160°F (71°C) and juices run clear.
Remove from the oven and let rest for 10 minutes to allow the sauce to thicken before serving.