Combine cilantro, chives, dill, capers, lemon zest, lemon juice, garlic salt, pepper and the flesh from 1 avocado in a food processor; process until finely chopped, about 30 seconds. Add mayonnaise and yogurt; process until smooth, 1 to 2 minutes.
Dice the remaining avocado and place in a medium bowl. Add chicken and the dressing; stir gently until combined and evenly coated. Serve at room temperature or refrigerate until cold, about 2 hours. Garnish with additional chives and lemon zest, if desired.
