drain the tuna. Add mayo and mustard to taste. Add dill relish, or a chopped dill pickle. Celery is also excellent for a crunch in there, need something that is crunchy to balance the tuna. Salt and Pepper to taste.
yzziM, holy sh-t, a cup of mayo, what in christ are you doing to yourself, or how big is a tuna "tin" in your area?? Plus, I've never dressed a salad with mayo, so I'm not sure about that stuff... :Q