In a large mixing bowl, combine the shredded chicken and chopped dill pickles.
In a separate bowl, mix together the mayonnaise, Greek yogurt, Dijon mustard, fresh dill, garlic powder, onion powder, salt, and pepper until well combined.
Pour the dressing over the chicken and pickles. Add the red onion and celery if using, and gently fold everything together until the chicken is evenly coated.
Taste and adjust seasoning if needed.
Cover the bowl and refrigerate for at least 30 minutes to allow the flavors to meld.
Serve chilled on a bed of lettuce, in a sandwich, or with crackers.