It used to be made with tuna packed in oil, but it is now almost always made with tuna packed in water for our more calorie-conscious society.
Canned tuna is always precooked.
For a slightly different spin on this old-time favorite, I have added curry powder and ginger to the dressing and packed the salad into a pita pocket rather than putting it between two pieces of regular bread. You can also use this same recipe for a curried tuna salad. Just add a couple of cups more lettuce and spoon it onto a chilled plate. When serving it as a salad, I usually sprinkle roasted peanuts over the top, garnish it with fresh fruit and serve toasted pita bread on the side. Add the onion, raisins, apple and lettuce and mix well.