Remove the top of the tomato and set aside. Use a paring knife and a spoon to carefully remove the insides of the tomato (discard or save for another recipe.)
Drain the oil from the tuna cans. Put the tuna and the remaining ingredients in a medium bowl and mix well.
Use a spoon to fill the tomatoes with tuna salad. Put the set side tomato tops on top of the tuna salad when serving.