Grilled Tuna Niçoise

4 cups cubed red potato (1 ¼ pound) ½ pound green beans, trimmed 1 - 8-ounce tuna steak ½ cup vertically sliced red onion ½ cup chopped fresh parsley 1 tablespoon chopped fresh tarragon ½ cup chicken broth 3 tablespoons white wine vinegar 1 tablespoon extra-virgin olive oil 1 tablespoon dijon mustard ¼ teaspoon salt ¼ teaspoon freshly ground black pepper 8 cups gourmet salad greens 1 cup cherry tomatoes, halved ¼ cup Niçoise olives 2 soft boiled eggs, cut in ½-inch slices

Cook the potatoes in boiling water for 6 minutes or until tender; remove with a slotted spoon. Add green beans to boiling water, and cook 3 minutes or until crisp-tender. Drain. Prepare grill or broiler. Place the fish on a grill rack or broiler pan coated with cooking spray; cook for 3 minutes on each side or until desired degree of doneness. Cut the fish into ¼ inch slices. Combine potato, fish, onion, parsley, and tarragon in a large bowl. Combine the broth and next 5 ingredient (broth through pepper); stir well with a whisk. Pour ½ cup broth mixture over potato mixture, and toss well. Divide beans, greens, tomatoes and eggs evenly among 4 plates. Top each serving with 1 ½ cups potato mixture and 1 tablespoon olives. Drizzle 1 tablespoon of remaining broth mixture over each serving.