This salad tastes best after it's marinated overnight in the fridge. You can use any vinaigrette you like, but my favorite is Dijon, red wine vinegar, and olive oil. Lemon juice and olive oil would be good too. Balsamic may be too sweet.
As for the tuna- high quality olive oil packed just tastes better, but water packed works too. I won't judge. Much.
You can serve this over bibb lettuce for a light entree, or eat it straight from the container, standing in front of the fridge, as I tend to do... —Helen