Place potatoes in 4-quart saucepot and cover with water. Add 2 teaspoons salt if desired. Bring to a boil over high heat.
Reduce heat to low and simmer, covered, 18 minutes or until potatoes are almost tender. Add green beans and simmer 2 minutes or until potatoes are tender and green beans are tender-crisp. Drain and cool.
In small bowl, combine mayonnaise, mustard, vinegar, salt and pepper.
Cut potatoes into 1-inch chunks. Combine potatoes and green beans in a large bowl. Toss with mayonnaise mixture until coated.
Stir in deviled ham spread and red onion. Sprinkle with parsley if desired, and serve or chill until ready to serve.