I also like to mash tuna in a ziploc bag. MUCH neater. I used to (MANY years ago) chop the tuna in my Bubby's old wooden chopping bowl with a hand chopper (looked like an axe with a handle). A pastry blender would do the same job, or even a potato masher.
Wow this thread just brought back some amazing memories to me. My dad, O"H would make school lunches for us whenever my mom O"H was in the hospital having a baby. he would chop up the tuna, add the mayo, and then spread the tuna on the bread. THEN he would put something totally off the wall in the sandwich, like say, peanut butter, babana slices, or raisins. When we would protest this sacrilegous ruin of a perfectly good tuna sandwich, he would remind us that our stomachs didn't care what was mixed together when it all got down there, and that tuna is healthy, peanut butter is healthy, and fruit is healthy, so we should be happy we had a well-rounded healthy meal.