You can serve the salad in a large bowl or on individual plates. If you are using a bowl, arrange the lettuces around the inside. If you are using salad plates, first toss the lettuces, tomatoes, bell pepper, and tuna separately with the remaining vinaigrette. Then arrange the lettuces on the salad plates. Arrange all the remaining ingredients—potato slices, beans, tomatoes, bell pepper, eggs, tuna, anchovies, and olives - decoratively on top of the lettuces in the bowl or on each plate. If serving at the table from the bowl, just before serving, pour the remaining vinaigrette over the salad and toss gently, then serve on plates.