Preheat oven to 350ºF.
Mix the chicken, taco seasoning, cream cheese, sour cream, mayonnaise, tomatillo salsa and cheese in a large bowl, reserving a quarter of the cheese for the top.
Pour the mixture into a 1 1/2-quart baking dish and top with the reserved cheese. (The recipe can be refrigerated or frozen at this point.)
Bake until the dip is bubbling on the sides and golden brown on top, about 20-30 minutes.
Top with the lime juice, red onion, scallions, lettuce, tomato, avocado, olives and cilantro (if using) and serve.