Preheat the oven to 375°F (190°C).
In a mixing bowl, combine the 10 oz red enchilada sauce, softened 8 oz cream cheese, and 1/2 cup sour cream; whisk or beat until smooth and uniform.
Place the 2 lb boneless skinless chicken breasts flat in a casserole dish in a single layer.
Pour the sauce mixture evenly over the chicken, then sprinkle 1 cup shredded sharp cheddar cheese over the top.
Bake uncovered at 375°F for 30–40 minutes, or until the internal temperature of the chicken reaches 165°F (74°C).
Remove from the oven and let rest for 5–10 minutes.
Top with pico de gallo, guacamole, additional sour cream, and chopped cilantro as desired, then serve warm.
