Place the potatoes in a pan with water covering them. Cook until they are fork tender, approximately 20 minutes. Cool completely, then toss with the olive oil, salt and pepper.
Cook the green beans for 6 minutes, then add to a bowl of ice water, to stop the cooking and keep them bright.
Lay the vegetables around a large plate touching each other, or slightly overlapping. Add the tuna and eggs.
Whisk all the dressing ingredients together and serve with the salad.