In a large bowl, mash chickpeas with the back of a wooden spoon or a potato masher until they are completely broken down. Add onion, garlic, egg, mustard, salt, and pepper. Mix until fully combined. Add flour, one tablespoon at a time, until there is no visible liquid but it is still relatively wet.
Heat canola oil in a cast iron skillet. Using your hands, form 6-8 fritters and drop them into the hot oil. Cook on each side for 3-6 minutes, until nicely browned, then flip and repeat on remaining side.
Meanwhile, stir together mayonnaise and Harissa.
Serve fritters with Harissa aioli.
Recipe by Things I Made Today at https://www.thingsimadetoday.com/2015/01/05/dijon-chickpea-fritters-harissa-aioli/