Put all vinaigrette ingredients in a screw top jar. Shake to combine.
Wash fingerling potatoes. Boil potatoes in lightly salted water for about 12 minutes until tender. Drain and toss with ¼ cup vinaigrette. Steam green beans for about 5 minutes. Plunge into cold water to stop cooking. Pan fry zucchinis in a single layer until lightly browned.
Arrange lettuce leaves in a single layer on a large platter. Place potatoes in the center and arrange mounds of beans, zucchinis, tomatoes, olives, tuna, and capers on either side of the plate. Just before serving, pour remaining vinaigrette all over salad.