Cook green beans in boiling salted water, 3-4 minutes.
Remove beans and add potatoes, simmering 15-20 minutes.
When potatoes are done, halve them and toss them in a bowl with the green beans and a few tablespoons of the dressing.
While beans and potatoes are cooking, heat a grill on high.
Grill tuna after coating in dressing and salt and pepper, on high heat to sear the outside of the steak while leaving the inside soft and pink, about 5 to 6 minutes, turning once.
Let tuna rest for a few minutes after cooking, then slice into strips.
Shred the lettuce by hand and toss wih a little dressing, then add to the plate, arranging tomatoes, eggs, potatoes, green beans, tuna slices and olives on top. Top with capers, basil, and a drizzle of vinaigrette dressing and serve.