Preheat the oven to 350°F degrees
In a small bowl, mash the avocados (to your liking) with salt, lime juice and garlic.
Stir the sour cream into the avocado mixture and stir well.Add the onions, tomatoes and cilantro, and then stir untilwell combined.
Add the chicken and gently fold to coat, and then adjust theseasoning as needed.
Arrange the taco shells on a baking sheet and add some cheese to each.
Bake for 3-5 minutes, or until the cheese is melted.
Remove from the oven, and fill the tacos with the lettuce and chicken salad.