Soak dried chickpeas in plenty of cold water for 8–12 hours; drain and rinse thoroughly.
Pulse the soaked chickpeas in a food processor until coarse crumbs form; avoid pureeing to a paste.
Add the chopped onion, garlic, parsley, cilantro, cumin, coriander, salt and pepper; pulse to combine into a coarse, slightly sticky mixture.
Scrape the bowl and pulse again so the mixture holds together when pressed but is not smooth.
Stir in baking powder and 2 tablespoons flour; add up to 1 more tablespoon flour if mixture is too wet.
Transfer the mixture to a bowl, cover and chill for 30–60 minutes to firm up for easier shaping.
Shape the mixture into small balls or patties (about 1.5 inches) using wet hands or a scoop for even sizes.
Heat 1–1.5 inches of oil in a skillet to around 350°F (175°C) for deep frying, or preheat oven to 400°F (200°C) for baking.
Fry a few falafel at a time, turning as needed, until deep golden and crisp, about 3–4 minutes per side; drain on paper towels. If baking, place on a tray, brush with oil and bake 20–25 minutes, turning once.
Serve hot with tahini sauce, pita, salad, and garnish with sesame seeds and chopped parsley.