Put the chickpeas in a large bowl and add enough cold water to cover them by at least 2 inches. Let soak overnight, then drain.
Place the drained, uncooked chickpeas and the onions in a blender. Add the parsley, cilantro, salt, chili flakes, garlic, and cumin. Process until blended but not pureed.
Transfer the mixture in a large bowl. add in the baking powder and 4 tablespoons of the flour, and mix with a spoon. Add enough flour so that the dough forms a ball and no longer sticks to your spoon. Place the bowl in the refrigerator, covered with film, for 2-3 hours.
Form the chickpea mixture into balls about the size of walnuts with wet hands.
Usually about 2 tbsp of mixture per falafel is enough but you can make them smaller or larger depending on your personal preference
Heat 3 inches of the vegetable oil in very high temperature in a deep pot or wok and fry 1 ball to test. If it falls apart, add a little flour.
Fry the balls for a few minutes on each side, or until golden brown. Drain on paper towels before serving.