Combine the chickpeas, salmon, onions, garlic, cilantro, cumin, salt and chili flakes in the bowl of a food processor and pulse until combined but still chunky, scraping down the sides of the bowl once or twice. Add the flour and baking powder and pulse until you have a soft mixture that you can roll into balls without sticking to your hands too much. You can make it as smooth as you want, but I like leaving a little texture.
Roll the dough into meatball-sized balls, and if you like, flatten each slightly, making a little patty. (I like doing this for maximum surface area, which equals more crunch. Flatter also means they cook through more quickly.)
In a shallow pot or skillet, heat about 1/2-inch of canola or other mild vegetable 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 the oil), until they’re golden and crisp. (You could get away with using just a drizzle of oil – if you do this, best to leave the falafels round, so that you can roll them around in the pan to brown all sides.) Transfer to a paper towel lined plate.
Serve warm, with tzatziki or thick plain Greek yogurt spiked with lemon, garlic, tahini and salt. Makes about 20 falafel.