2. Preheat the grill.
3. Grill each steak for about 3 minutes on each side, depending on the thickness of the tuna.
4. Remove the steaks to a warm platter.
5. Meanwhile bring a large pot of well-salted water to a boil. Have a bowl of ice water at hand. Add the green beans to the boiling water and blanch to the desired degree of doneness, about 2 to 4 minutes depending on their size. Remove the green beans with a slotted spoon and immediately plunge them into the ice water. Drain and set aside.
6. Add the potatoes to the boiling water and cook until they are tender when pierced with a fork. Drain and set aside.
7. Toss the spinach with half of the vinaigrette just to coat the leaves. Place the spinach on chilled plates or in large shallow bowls.
8. To assemble the salad, slice the tuna into strips and put it on top of the spinach. Place the green beans, potatoes, cherry tomatoes and olives around the tuna and drizzle with the remaining vinaigrette.