Add all ingredients except cornstarch and green onion to instant pot. Lock lid, set valve to sealing. Program for poultry, and increase time to 25 min. NPR. When the pin drops, open the lid and shred chicken. Remove 1/4 cup cooking liquid from slow cooker. Mix with cornstarch and return to IP. Push sauté. Stir well. Bring to a boil and hit cancel. Stir frequently with heat element off until sauce is thickened. Garnish with green onion.