Mix margarita mix, lime rind, minced garlic, cumin, salt and pepper. Add chicken and marinate approximately one hour. Grill or smoke the chicken until cooked. Cool and coarsely chop if you are ready to make the salad. If not, wrap and refrigerate chicken breasts until ready to continue, then chop it up.
Make dressing by combining mayonnaise, sour cream, minced garlic, cayenne pepper, lime juice, onion, cilantro, salt and pepper. Whisk ingredients together. Stir in chicken.
To serve, layer tomatoes, then chicken salad and top with sliced avocado. Squeeze the other half lime over the avocado to keep it from turning brown.
Top each serving with a sprig of cilantro. This amount makes approximately two large servings, depending on the size of your chicken breasts.