Thinly slice ½ red onion and pour over boiling water, apple cider vinegar, maple syrup, salt, bay leaf, and black peppercorns.
Mash the chickpeas with a fork until flaky.
Add the pickle, celery, onion, nori, mustard, vegan mayo, and salt to the mashed chickpeas. Mix well.
Toast the bread.
Layer arugula on both slices.
Add the vegan “tuna,” avocado, tomato, and pickled red onion to one slice.
Top with the second slice of bread.
Slice and enjoy.
