Humble in parts yet rich in textures, this combination of flaky tuna, creamy beans, juicy raw onion and hearty kale makes a satisfying and quick lunch. Massaging the kale and onion with lemon juice and salt softens and seasons so that the kale remains toothsome but not tough, and the onion spicy but not prickly. The salad can be made up to two days ahead and is amenable to improvisation: Add cooked grains, thinly sliced tomatoes or cucumbers or leftover roasted vegetables.
