Put the potatoes in a large saucepan, add water to cover and a nice pinch of salt; bring to a boil over medium heat.
Simmer the potatoes for 12 minutes to give them a head start, and then add the eggs.
Place a steamer basket or colander on top of the simmering water. Put the green beans in the steamer and cover with a lid. Steam the beans for 5 minutes until crisp-tender while continuing to cook the potatoes until fork tender.
Drain out the water and put the potatoes, eggs, and green beans in a colander; rinse briefly under cold water.
Peel the shells off the eggs and cut them in 1/2 lengthwise.
Place a large skillet over medium-high heat. Rub the tuna on all sides with olive oil, and a bit of the vinaigrette; season with a fair amount of salt and pepper.
Lay the tuna in the hot pan and sear for approximately 2 minutes on each side; as the tuna cooks, the red meat will become whiter. Transfer the tuna to a cutting board and slice.
To assemble the salad: combine the potatoes, green beans, tomatoes, olives,anchovies, capers, and chives in a large mixing bowl. Take the vinaigrette and give it another good shake to recombine. Drizzle the salad with enough vinaigrette to fully moisten and toss gently to coat; season with salt and pepper. Place lettuce on a platter and arrange all the ingredients.
Combine all ingredients in a mason jar. Screw the cap on the jar and shake the vinaigrette vigorously to emulsify. Set the dressing aside while preparing the salad so the flavors can marry.