In a food processor, combine the chickpeas, scallions, garlic, cumin, coriander, cayenne, parsley, cilantro, egg, and lemon juice. Pulse to combine and season with salt. The mixture will not be smooth, but it should not have large chunks.
Add in the baking powder and 1/3 cup of the flour and pulse to just combine. Remove to a bowl and chill in the refrigerator for 30 minutes.
Remove the chickpea mixture from the refrigerator. Add enough oil to a large saute pan so it reaches 1/2-inch up the sides and heat it over medium-high heat until an inserted thermometer reads 360 degrees F.
Meanwhile, drop spoonfuls of the chickpea mixture onto a plate with 1/4 cup flour. Roll into balls on the floured plate and press gently into patties. Fry in batches of hot oil for about 3 to 4 minutes each side and drain on paper towels.
Serve the falafel on a bed of lettuce with chopped salted tomatoes, grated cucumber and White Bean Yogurt Sauce.