Prepare the Vegetables: In a large pot of salted boiling water, cook the potatoes until tender, about 10-15 minutes. Add the green beans to the same pot during the last 3 minutes of cooking. Drain the vegetables and immediately plunge them into a bowl of ice water to stop the cooking and preserve their vibrant color. Once cooled, drain them again and set aside.

Make the Vinaigrette: In a small bowl, whisk together the olive oil, red wine vinegar, Dijon mustard, and minced garlic. Season with salt and black pepper to taste.

Prepare the Tuna and Eggs: If using canned tuna, drain it well and flake it into large pieces. If using fresh tuna, sear it in a hot pan for 2-3 minutes per side. Prepare your hard-boiled eggs and slice them into quarters.

Assemble the Salad: Arrange the lettuce leaves on a large platter or in a shallow bowl. Artfully arrange the cooked potatoes, blanched green beans, tomato wedges, sliced red onion, olives, and hard-boiled eggs over the lettuce. Add the tuna and anchovy fillets (if using) in their own sections.

Serve: Drizzle the vinaigrette evenly over the entire salad. Serve this gorgeous tuna niçoise salad immediately while the vegetables are still fresh and the flavors are at their peak.