Whisk together the lemon juice, capers and Dijon mustard in a large bowl. While continuing to whisk, drizzle in the olive oil in a steady stream. Whisk in 1/4 teaspoon salt. Add the beans to the dressing and mash gently with a spoon. Add the tuna, flaking it with a fork into bite-size pieces. Toss lightly to coat. Top the tuna mixture with the arugula, treviso, endive, shaved fennel, parsley leaves and 1/2 teaspoon salt. Using your hands, toss the salad together, bringing the dressing up from the bottom of the bowl until everything is coated evenly.
Recipe courtesy of Giada De Laurentiis