Chicken Soup with Orzo Ingredients: 1 tablespoon olive oil 1 medium leek, white and pale-green parts only, sliced crosswise 1/2-inch thick 1/2 cup onion, diced 2 cloves garlic, minced 1 celery stalk, sliced crosswise 1/2-inch thick 4 Chicken thighs, boneless, skinless, and trimmed of excess fat 8 cups of chicken stock Zest of 1