I'm not a big fan of mayonnaise based tuna salad, so I've been developing this concoction over many years and I think it's just delicious now. After spending some time in Southern France I came up with this thyme/olive oil/balsamic based recipe. I actually get excited when I think I might make it for lunch. The only problem with leaving out the mayonnaise, and including the crucial two ribs of celery, is that the mixture tends to fall apart rather easily, which is not desirable when making sandwiches. To remedy this, I advise you to dice the vegetable ingredients as small as possible, to add plenty of olive oil (its great for your health and not fattening, so pour it on!) and to mash up the tuna chunks with the back of a fork well before mixing all the ingredients.
Try making this into a yummy salad just by topping a bed of butter lettuce or red leaf with a large scoop of the mixture. No need to add dressing.
Crostinis are equally easy. Simply brush slices of baguette with olive oil and bake for a few minutes (don't take your eyes off of them!), then put a teaspoon or two of the mixture on top of each one. Et voilà!