Soak dried chickpeas overnight in a large bowl filled with water.
The next day, drain the chickpeas and pulse in a food processor until crumbly and there are no whole chickpeas left. Transfer to a large bowl.
In the same food processor, pulse together the onion, garlic, parsley and cilantro. Pulse until it almost looks like a paste. Add parsley mixture to beans.
Use a large spatula to mix the beans and herbs together. Add cumin, cayenne, salt, pepper and flour. Mix well. Add baking powder and soda just before frying. Mix everything well.
Heat a large skillet with vegetable oil and bring oil up to about 370 degrees F. You can test to see if the oil is hot by dropping a small piece of batter. If it sizzles, it's ready.
Use a large tablespoon and form batter into balls. I scoop about 2 tablespoons worth and form a ball between your hands.
Carefully place the falafel in the hot oil. You can fit 4-5 in at once but don't overcrowd the pan. Fry on 1 side until you can see it browning on the sides, about 4-5 minutes. Then flip over and fry other side.
The falafel should be crisp on the outside and soft on the inside. To make tahini yogurt, just mix tahini and Greek yogurt together.