If using a food processor, you can add the chickpeas, onions and pickles all at once and pulse until pieces are uniform and small. Then transfer to a bowl.
In a bowl, mash chickpeas until all of them are flattened. You want them to be chunky for the texture but not whole.
Otherwise, to the bowl, add finely chopped red onion and pickles and mix to combine.
Add pickle brine and mayo and mix until well combined. Taste test to make any adjustments to the tanginess if needed. Season with salt & pepper to taste.
Keep in refrigerator. Keeps for up to 7 days.