In a dish inspired by salade Nicoise, grilledyellowfin tunasteaks are accompanied by a chopped salad of green beans, tomatoes, and black olives.
Cover potatoes with cold water in a medium saucepan; add salt. Bring to a boil; cook until potatoes are tender, 10 to 12 minutes. Drain, and rinse under cold running water. Cut potatoes into 1/4-inch-thick slices; transfer to a large bowl.
Prepare an ice-water bath; set aside. Bring a medium saucepan of water to a boil. Add haricots verts; cook until almost tender, 4 to 5 minutes. Plunge haricots verts into ice-water bath; let cool completely. Drain, and cut haricots verts in half. Add to bowl with potatoes. Add tomatoes, anchovies, olives, basil, oil, and lemon juice; season with salt and pepper. Toss to combine, and set aside.
Preheat grill to high (if using a charcoal grill, coals are ready when you can hold your hand 5 inches above grill for just 2 seconds). Season tuna with salt and pepper. Grill tuna, turning once, 3 minutes per side for rare. Transfer to a cutting board; slice tuna against the grain. Grill bread, turning once, until slightly charred. Serve tuna with salad and bread.