In a large mixing bowl, combine the Greek yogurt, Dijon mustard, garlic powder, and a pinch of salt and black pepper. Stir until smooth.

Add shredded chicken, sliced pepperoncini, chopped celery, and diced red onion. Gently fold to combine.

Taste and adjust seasoning; add more salt or pepper if needed.

Cover and refrigerate the salad for 15 to 30 minutes to allow flavors to meld.

Serve in lettuce cups, on whole grain bread, or with crackers, garnished with parsley or dill.