Prepare the Tzatziki: Mix Greek yogurt, cucumber, garlic, olive oil, and dill in a bowl. Season with salt and pepper to achieve a smooth, creamy consistency.Assemble the Salad: Toss romaine lettuce, tomatoes, pepperoncini, olives, and red onion in a large salad bowl.Add Chicken: Layer the chicken over the salad base.Dress with Tzatziki: Dollop the tzatziki over the salad and chicken.Garnish: Sprinkle crumbled feta cheese on top.