Tuna salad starts with a blend of two main ingredients: tuna and mayonnaise. the tuna used is usually pre-cooked, canned, and packaged in water or oil. pickles, celery, relish, and onion are foremost among the ingredients that are often added. when the mixture is placed on bread, it makes a tuna salad sandwich. tuna salad is also regularly served by itself, or on top of crackers, lettuce, tomato, or avocado. chopped boiled eggs may be added. relish adds a piquant flavor yet, unlike commonly added vegetables, requires no chopping.

Source: Wikipedia