Increase the heat of your oil to 350F (180 C) . As the oil is heating, make your batter:
In a large bowl, combine flours, baking powder, salt, pepper, and onion/garlic powders.
Add egg and beer, stir well to form a thick batter. Allow batter to sit for 5 minutes or so, to soften the bean flour.
After 5 minutes, check the batter consistency - it should drip easily off a spoon. Thick batter will make a thick coating on the fish, a thinner batter will make a lighter and crispier coating - feel free to thin with a little more beer or water if you’d like.
As pictured in the process shots, this is the thicker end of what you want the batter to look like.
Pat the fish dry with paper towels, season on both sides with a little salt and pepper.
Gently dredge fish in garbanzo flour, shaking excess chickpea flour back into the bowl.
One piece at a time, dip fish into batter, allowing excess batter to drip back into bowl for a few seconds, before carefully transferring to heated oil.
Fry for a few minutes on each side, until golden brown and cooked through.
Use a slotted metal spoon to transfer fried fish to paper towels.