Tuna Bean Salad

One 15-ounce can chickpeas, rinsed and drained One 15-ounce can red kidney beans, rinsed and drained 6 ounces green beans, trimmed and sliced into 1/4-inch rounds 1/2 medium onion, finely chopped (about 1/2 cup) 12 sweet piquante peppers, such as Peppadews, chopped, plus 2 tablespoons brine 2 tablespoons freshly squeezed lemon juice (from 1 lemon) 2 tablespoons extra-virgin olive oil Kosher salt and freshly ground pepper 1 cup plain yogurt 1/4 cup tahini 1 large head red leaf lettuce, chopped (about 12 ounces) Two 5-ounce cans white albacore tuna in oil, drained 1/2 teaspoon smoked paprika