Place the drained chickpeas in a medium mixing bowl. Mash them with a potato masher or the back of a sturdy fork until most are broken down. Leave a few chickpeas partially whole for additional texture.
Scoop the ripe avocado into the bowl and mash it into the chickpeas until evenly distributed.
Add the freshly squeezed lemon juice and minced garlic.
Add the diced celery, chopped dill pickles, fresh dill, and green onions.
Season with a pinch each of sea salt and freshly ground black pepper.
Stir thoroughly until all the ingredients are evenly combined.
Taste and adjust the seasoning with additional lemon juice, salt, pepper, dill, or pickles as desired.
Spread mustard over slices of whole grain bread, if using.
Divide the Smashed Chickpea Avocado Sandwich filling between the bread slices.
Add lettuce or arugula and finish with the remaining bread. Serve immediately.