Soak the garbanzo beans overnight in water, or at least for several hours. They should double in size.
Drain and rinse them well. Then add them to your food processor along with the chopped onion, garlic cloves, parsley, salt, cumin, turmeric, black pepper, and cayenne pepper.
Process the ingredients together until you get a coarse meal. Scrape the sides down periodically and keep mixing until you start to get more of a paste so that the mixture will hold together more easily.
Add some oil to your frying pan, and begin heating it over medium heat.
While the oil is heating, form a trial falafel by either using wet hands to form a small patty, or you can use two spoons together or a falafel scoop. I usually use the two spoon method, and don't like to make them too big. Smaller falafel hold together better, and are more likely to completely cook through.
If you have a hard time getting the falafel to hold together, you can first try processing your mixture in the food processor for longer to get more of a paste.
If they still don't come together well, you can add in some flour and/or an eggs, depending on your diet, to help bind them together.
Finish forming all of your falafel, and fry them in the oil until they reach a golden brown color on both sides.