Place 1/2 cup water, orange juice concentrate, barbecue sauce, chipotle pepper, salt and garlic powder in a blender; cover and process until blended., Place chicken and onion in a 6-qt. electric pressure cooker; top with juice mixture. Lock lid; close pressure-release valve. Adjust to pressure-cook on high for 6 minutes., Quick-release pressure. A thermometer inserted in chicken should read at least 165°. Remove chicken from pressure cooker; keep warm., In a small bowl, mix cornstarch and remaining 2 tablespoons water until smooth; gradually stir into pressure cooker. Select saute setting and adjust for low heat. Simmer, stirring constantly, until thickened, 1-2 minutes. Spoon over chicken; top with orange zest.