In a large saucepan or medium stockpot combine chicken, celery, onion, garlic, parsley, lemon zest, mint sprigs, crushed red pepper, and water. Bring to a boil, skim, reduce heat, and continue to simmer for 45 minutes, or until chicken is tender. Strain stock through a fine sieve. Transfer chicken to a plate to cool and discard remaining vegetables. Return stock to saucepan, and continue to reduce until broth is flavorful. Add rice to stock and continue to cook until rice is tender. When chicken is cool enough to handle, remove meat from bones and tear into bite-sized pieces. Add to broth and rice and cook for 3 to 4 minutes. Add lemon juice, mint and salt and pepper, to taste and let cook for 2 to 3 minutes. Serve immediately, garnished with lemon slices and sprigs of mint if desired.