Place the dry chickpeas in a medium bowl and cover with water. Let soak at room temperature for at least 12 hours, or up to 24 hours. The chickpeas will double in size. Drain, rinse, and dry the chickpeas thoroughly—using a salad spinner helps. In a food processor, pulse the chickpeas and salt to coarse, pebble-sized bits. Add parsley, cilantro, onion, garlic, cumin, coriander, and black pepper. Process until a thick, textured paste forms, scraping the bowl as needed. Remove the blade, cover the bowl, and refrigerate the mixture for 1 hour to firm up. After chilling, sprinkle the baking powder over the falafel batter and gently fold it in. Line one baking sheet with parchment paper and another with paper towels. Using a cookie scoop or your hands, scoop and firmly roll about 1½ tablespoons of the mixture into balls and place on the parchment-lined sheet. Heat 1 inch of oil in a large, high-sided skillet over medium heat. When a bit of batter sizzles on contact, add 10–12 falafel to the oil, avoiding overcrowding. Fry 3–3½ minutes per side, until golden brown and crispy. Transfer to the paper towel-lined tray. Repeat with the remaining mixture. Serve the falafel warm with tahini sauce for dipping.