Combine potatoes and water to cover in a large saucepan; bring to a boil over medium heat, and cook for 13 minutes. Add green beans, and cook 7 minutes or until potatoes are tender. Drain and rinse with cold water. Cut each potato into 8 wedges.
Whisk together vinegar and next 6 ingredients in a large bowl; add potato wedges and green beans, tossing gently to coat. Cover and chill 2 hours. Garnish, if desired.