Spring nicoise salad

1. Bring 1 quart water to boiling in a 10-inch skillet.
2. Add the potatoes and cook, covered, for 8 minutes or until almost tender.
3. Add green beans and cook an additional 5 minutes.
4. Place yogurt and basil in bowl of blender and whirl for process for 30 seconds.
5. Set aside.
6. Line four plates with lettuce; top evenly with potatoes, green beans, onion slices, tuna, and egg slices.
7. Garnishi with olives.
8. Drizzle each salad with 2 tablespoons yogurt dressing.