Add one avocado, mayonnaise (or Greek yogurt), lemon juice, parsley, chives, dill, garlic, salt, and black pepper to a food processor or blender.
Blend until completely smooth, scraping down the sides as needed.
Transfer the dressing to a large mixing bowl.
Add the chopped chicken, celery, and the remaining diced avocado.
Gently fold everything together until evenly coated with the creamy dressing.
Taste and adjust seasoning if needed.
Cover and refrigerate for at least 20 minutes before serving for the best flavor.
Serve your Green Goddess Chicken Salad with crackers, pita chips, lettuce wraps, or toasted bread.