A great way to serve this salad is to slice a 9-inch round focaccia in half horizontally, fill it with the tuna, and press a plate down on top of the round bread. Place a heavy can or weight on top for an hour, and the dressing will seep into the bread. Slice and serve.
Put all of the ingredients into a large bowl and gently fold together until well combined. Serve on sliced bread as a sandwich or over a green salad.