In a large mixing bowl, combine 1 cup of Greek yogurt, 2 tablespoons of Dijon mustard, 1 teaspoon of garlic powder, and a pinch of salt and black pepper. Whisk until smooth and creamy.

Add 2 cups of shredded cooked chicken breast to the dressing mixture. Gently fold until evenly coated.

Incorporate 1 cup of sliced pepperoncini peppers, 1 cup of diced celery, and ½ cup of finely chopped red onion to the chicken mixture. Mix gently.

Give the mixture a taste and adjust the seasoning with salt or black pepper as needed.

Cover the bowl with plastic wrap and refrigerate for about 15-30 minutes to allow flavors to meld.

Serve the salad chilled on toasted whole-grain bread, in lettuce cups, or over a bed of mixed greens.