This chickpea tuna is one of my favorite recipes. It just happens to be incredibly easy to make. Use a food processor to make the mash. If you don’t have one the best option is to mash the chickpeas with a fork. Be sure to mince the celery if you plan on doing that. A food processor will not work as well as a food processor. Ume plum vinegar can be found at health food stores like Whole Foods, or online. It is about $3.50 a bottle, so not very expensive. It's super salty and has a special tang that really elevates this recipe. If you don't have any you can use apple cider vinegar or white vinegar.