MICROWAVE potatoes and water in covered microwaveable dish on HIGH 7 min. or until potatoes are tender. Meanwhile, heat oil in large saucepan on medium-high heat. Add chicken; cook 7 min. or until evenly browned, stirring occasionally.
ADD potatoes, soup, dressing and frozen vegetables to chicken in saucepan; stir. Bring to boil; cover. Simmer on medium-low heat 3 min. or until chicken is done and vegetables are heated through.
STIR in sour cream; cook 1 min. or until heated through, stirring occasionally.