Soak the chickpeas in plenty of water for 8 hours, then drain and dry them well.
Pulse the chickpeas, onion, garlic, parsley, cilantro, cumin, coriander, baking powder, lemon juice, and salt in a food processor until coarse and crumbly.
Chill the mixture for 30 minutes, then shape it into small balls or thick patties.
Heat the oil to 175°C / 350°F and fry the falafel in batches for 3 to 4 minutes per side until deep golden and crisp.
Make the Sauce and Serve:
Whisk tahini, lemon juice, garlic, and water until smooth and pourable, adding a little more water if needed.
Drain the falafel on a rack or paper towels and serve hot with tahini, pita, salad, and pickles.
Notes
Use dried chickpeas rather than canned for the best texture.
For a lighter option, bake shaped falafel at 220°C / 425°F until browned, turning once.