To grill the tuna, get a charcoal or stove-top cast iron grill very hot. Brush the fish with olive oil, and sprinkle with salt and pepper. Grill each side for only 1 1/2 to 2 minutes. The center should be raw, like sushi, or the tuna will be tough and dry. Arrange the tuna, haricots verts, potato salad, tomatoes, eggs, olives, watercress, and anchovies, if used, on a large flat platter.
For the vinaigrette, combine the vinegar, mustard, salt, and pepper. Slowly whisk in the olive oil to make an emulsion. Drizzle some over the fish and vegetables and serve the rest in a pitcher on the side.
French Potato Salad:
Yield:Cooking time: 30 minutes
Drop the white and red potatoes into a large pot of boiling salted water and cook for 20 to 30 minutes, until they are just cooked through. Drain in a colander and place a towel over the potatoes to allow them to steam for 10 more minutes. As soon as you can handle them, cut in 1/2 (quarters if the potatoes are larger) and place in a medium bowl. Toss gently with the wine and chicken stock. Allow the liquids to soak into the warm potatoes before proceeding.
Combine the vinegar, mustard, 1/2 teaspoon salt, and 1/4 teaspoon pepper and slowly whisk in the olive oil to make an emulsion. Add the vinaigrette to the potatoes. Add the scallions, dill, parsley, basil, 1 1/2 teaspoons salt, and 1/2 teaspoon pepper and toss. Serve warm or at room temperature.