Using a fork or potato masher, crush chickpeas in a large bowl until most are mashed but some are still whole. Add 6 tablespoons yogurt, ⅓ cup cranberries, the chopped celery, ¼ cup pecans, ¼ cup grapes, 2 tablespoons mayonnaise, 1½ tablespoons chives, 1 tablespoon dill, 1½ teaspoons mustard, 1½ teaspoons vinegar, ¼ teaspoon salt and ⅛ teaspoon pepper; fold to combine.
Divide the chickpea mixture among 4 toast slices. Top each with a lettuce leaf and another toast slice.
