In a large mixing bowl, combine the shredded chicken and mashed avocado. Mix until well combined.
Add the Greek yogurt, Dijon mustard, lemon juice, garlic powder, onion powder, salt, and pepper to the bowl. Stir until the mixture is smooth and creamy.
Fold in the chopped celery, red onion, and cilantro (if using) until evenly distributed.
Taste and adjust seasoning if necessary, adding more salt, pepper, or lemon juice as desired.
Chill the salad in the refrigerator for at least 30 minutes to allow the flavors to meld.
Serve on a bed of greens, in a sandwich, or with whole-grain crackers.