If using dry chickpeas, pour chickpeas into a large bowl and add enough cold water to cover them by at least 2 inches. Let soak overnight, then drain. Or use canned chickpeas, drained.
Place the drained, uncooked chickpeas and the onions in the bowl of a food processor fitted with a steel blade. Add the parsley, cilantro, salt, hot pepper, garlic, and cumin. Process until blended but not pureed.
Add baking powder and 4 tbsp. of flour, and pulse. You want to add enough flour so that the dough forms a small ball and no longer sticks to your hands. Turn into a bowl and refrigerate, covered for several hours.
Form the chickpea mixture into balls about the size of walnuts, or use a falafel scoop, available in Middle Eastern markets.
Heat 3 inches of oil to 375 F in a deep pot or wok and fry 1 ball to test, if it falls apart, add a little more flour to the mixture. Then fry about 6 balls at once for a few minutes on each side, or until golden brown. Drain on paper towel.
To assemble falafel sandwiches, fill half a pita with falafel balls, chopped tomatoes, onion, green pepper, and pickled turnips. Drizzle with tahini thinned with water.
FUN FACTS: 1. Egyptians omit the cilantro and substitute fava beans for the chickpeas. 2. Tahini (also called tahini) is an oily paste made from ground sesame seeds. It is available in Middle Eastern markets. 3. To garnish your falafel in true Israeli style, try adding one or several of the following condiments: Harrissa hot sauce, pickled turnips, mango amba (pickled), or sauerkraut.