Here's another one of my so-easy-it's-foolproof,
What you need:
Open the can and drain out as much of the water as
possible. Put it in a bowl and, with a fork, pull the
tuna chunks apart. Dump in a tablespoon of relish, a tablespoon
or two (depending on your taste and calorie-consciousness)
of mayo, and a handful of lettuce cut up into very small
bits. (As the lettuce is for texture, I like to use
the thicker part near the base of the leaf.) Mix it
all up. Taste. Add more of anything you want more of.
Spread on a piece of bread, cover with another piece
of bread, and eat.
When packing this in a bento, I strongly suggest
putting the tuna salad in some sort of container rather
than making the sandwiches ahead of time, as the
bread will get soggy, especially if you like mayonnaise.