Cut chicken breasts into 1 inch cubes. Place chicken, onion,carrots, celery, cilantro, green onion, garlic, salt, pepper and water in pressure cooker. Lock lid into place. Over high heat, bring cooker up to pressure. Then reduce heat to maintain pressure and pressure regulator rocks gently. Cook for 8 minutes. Quickly release the pressure. Carefully remove lid and add frozen corn. Heat on medium heat until corn is tender.