In a medium bowl, mash all of the chickpeas with a potato masher until almost all of the beans are broken down. A few whole chickpeas left is ok.Add the rest of the ingredients except mayo, mix well with a spoon.Add mayo (more or less to taste), mix well. Taste and adjust the seasoning: adding more kelp will make chickpea salad taste more like tuna; more pickles will make it saltier.At this point, you can either let the chickpea salad rest in the fridge for at least an hour to let the flavors blend together, or serve it right away if you're pressed for time. I sometimes make the salad the night before I intend to serve it for lunch. The salad will keep in the fridge for 2-3 days.Toast bread slices (2 per sandwich). Spread sliced avocado on the top slices, cover with sprouts (if using) and lettuce/spinach leaves. Spread as much chickpea salad as you like on the bottom bread slices. Put both slices together to close the sandwich; enjoy!