Put the chickpeas, onion, garlic, parsley, cilantro, cumin, salt, and chili flakes in the bowl of a food processor and pulse until combined but still chunky.
Add the flour and baking powder and pulse until you have a soft mixture that you can roll into balls without it sticking to your hands. Add another spoonful or so of flour if you need to.
Roll the dough into meatball-sized balls, and if you like, flatten each into a little patty.
In a shallow pot or skillet, heat about 1/2 inch of canola oil until it's hot but not smoking.
Test it with a bit of falafel mixture or a scrap of bread--the oil should bubble up around it.
Cook the falafel for a few minutes per side without crowding the pan (which will cool down from the oil), until they're nicely golden.
You can get away with using just a skiff of oil. If you do thsi, it is best to leave the falafel round so you can roll them around in the pan to brown all sides. Transfer to paper towels.
Serve in pitas with tzatziki, chopped cucumber, purple onion, and tomato.