In a bowl, mix everything together except the cucumber. (Salt + Pepper to taste)
If you are skipping the bread and want to serve on cucumber - cut your cucumber into bite size pieces. I made mine vary in height. Cut out a bit of the core, making it a little tiny "bowl" for the tuna salad. If you want to make them even prettier, cut slits in the cucumber skin.
Put a spoonful of tuna salad on the cucumber slices. Plate and serve.
Recipe by 2 Cats and Chloe at http://www.2catsandchloe.com/2015/05/tuna-salad-cucumber-bites-whole30.html