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

Fold in shredded chicken, sliced pepperoncini, diced celery, and finely diced red onion into the dressing, mixing until well-coated.

Taste the salad and adjust seasoning with more salt, pepper, or a splash of pepperoncini brine to suit your preference.

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

Serve the salad in lettuce cups, on whole-grain bread, or over mixed greens.