Bring a large pot of water to a boil; add chicken breasts to water and cook until chicken is no longer pink in the center and the juices run clear, about 20 minutes. An instant-read thermometer inserted into the center should read at least 165 degrees F (74 degrees C). Cool chicken and shred with a fork.
Stir ranch dressing, Mexican cheese blend, cream cheese, and hot pepper sauce together in a bowl with a fork until well-combined; add chicken and stir. Spread chicken mixture into a 9x13-inch baking dish.
Bake in the preheated oven until hot and bubbling, 15 to 20 minutes. Cool to room temperature; top with lettuce and tomato.