Cover potatoes with water in 4-quart sauce-pot, adding salt, if desired. Bring to a boil over high heat. Reduce heat to low and simmer 8 minutes. Add green beans and simmer 5 minutes or until potatoes are tender. Drain and rinse with cold water until completely cool.
In large bowl, combine all ingredients. Serve chilled or at room temperature and, if desired, on green leaf lettuce.