Place the potatoes in a pot and cover with water. Bring to a boil. Simmer about 30 minutes until very tender when pierced with a fork. Carefully drain and allow to cool. Peel and cut into 1/2 inch dice.
Blanch the green beans for about 5 minutes in a pot of water. Drain and rinse beans in cold water. Drain well.
Lightly toss potatoes, beans, onion, and hard boiled eggs.
Whisk olive oil, mayonnaise, lemon juice, parsley, salt, and pepper.
Add dressing to salad, toss and chill until ready to eat.