Drain and rinse the chickpeas, reserving about 3-4 tablespoons of the liquid. Dry the chickpeas well and set aside.
Drizzle 1 tablespoon of the reserved liquid over the bread and allow it to soak in. Squeeze the bread dry, then put the bread and chickpeas into a food processor and process until a soft paste forms. You may need to do this in batches. Transfer the mixture to a large bowl.
Put the onion into the processor and process until finely chopped. Add the chopped onion to the chickpea mixture. Process the garlic and cilantro until finely chopped and add them to the chickpea mixture. Add the coriander, cumin, salt and cayenne pepper to the mixture and season to taste with pepper. Stir to combine. Sprinkle the flour and baking powder over the mixture. Use your hands to mix until a soft dough forms, adding more of the reserved liquid if necessary.
Use wet hands to shape the mixture into walnut-size balls and set them on a baking sheet. Felafel can be prepared ahead of time to this point, then refrigerated until time to cook.
Heat 3 inches of vegetable oil in a deep-fat fryer or wok to 350 - 375°F or until a cube of bread browns in 30 seconds. Working in small batches, slide the balls into the oil and cook for 2-3 minutes or until a rich golden brown colour, turning to colour evenly. Use a slotted spoon to transfer the balls to paper towels and allow to drain.
Serve warm in pita bread with salad, hot pickles and Tahini. Use 3 balls per pita.