To prepare dressing, combine first 8 ingredients, stirring well with a whisk.
To prepare salad, place potatoes in a saucepan; cover with water. Add 1 teaspoon salt to pan; bring to a boil. Reduce heat, and simmer 10 minutes or until almost tender. Add beans, and cook an additional 4 minutes or until beans are crisp-tender. Drain. Rinse with cold water; drain well.
Quarter potatoes. Place the potatoes, beans, chicken, onion, and greens in a large bowl. Drizzle with dressing; toss gently to coat. Serve immediately.