I make this all the time, and it is good. You can use any onion for the red onion, depending on what you have. I usually use green onions, but even shallots or well-washed leeks will work. Sometimes, I'll add chopped eggs, olives, capers, or pickle relish for variety. Tarragon or basil are nice in this, but if you are using basil, make sure to eat it soon or it will darken. You can use chicken, canned salmon, shrimp, hard-boiled eggs, ham, leftover roast beef, or just about any simply prepared cooked protein in place of the tuna. It's a formula for luncheon salad as much as it is a recipe.
