Place the dry chickpeas in a medium bowl, cover with water by a few inches, and let them soak at room temperature for 12 to 24 hours until they double in size.
Drain and rinse the soaked chickpeas, then dry them thoroughly using a towel or salad spinner so the mixture doesn’t get too wet.
Add the chickpeas and salt to a food processor and pulse until they break down into coarse, gritty bits.
Toss in the parsley, cilantro, onion, garlic, cumin, coriander, and black pepper, then blend until you’ve got a thick, green-flecked paste (you might need to scrape the bowl a few times).
Take out the blade, cover the bowl, and chill the falafel mixture in the fridge for an hour so it firms up and holds its shape.
Sprinkle the baking powder over the chilled batter and gently fold it in until fully combined.
Line a baking sheet with parchment paper and another with paper towels, then scoop out about 1½ tablespoons of the mixture at a time, rolling each into a ball and placing it on the parchment.
Heat about 1 inch of neutral oil in a deep skillet over medium heat, and once it’s hot enough to make a test piece sizzle, fry the falafel in batches for 3 to 3½ minutes per side until golden and crispy.
Transfer the cooked falafel to the paper towel-lined tray and keep frying until they’re all done, then serve warm with tahini sauce.