Rinse chickpeas, place in a large bowl and cover with at least 3 inches cold water. Cover and let stand at room temperature overnight. They will almost triple in size so you will have about 4 1/2 cups. When ready, rinse and drain well.
To the bowl of a large food processor, add chickpeas, onion, herbs, scallions, garlic, flour, cumin, coriander, salt and pepper. Pulse the mixture, scraping down the sides every few presses, until it looks almost like cracker meal or couscous. You don't want it to turn into a paste but you don't want it too coarse either (approximately 15 to 20 3-second pulses). Just keep pulsing, scraping and checking until it looks right. Transfer mixture to a bowl, cover with plastic wrap and place in refrigerator for 1 to 2 hours.
After mix is chilled, dissolve baking soda in 2 teaspoons cold water, and stir into the mixture. Stir in sesame seeds. Scoop out about 1 1/2 tablespoons of the mixture and gently shape it into a ball and place on a tray. Continue until all of the balls have been formed.
Fill a deep 8 or 10-inch cast iron skillet, nonstick skillet or Dutch oven with 1 inch of oil. Heat over medium-high heat until oil registers 375°F on an instant-read thermometer. Carefully lower a few balls into oil one at a time, allowing some room between each. Adjust heat as necessary to maintain an even temperature and allow to fry, undisturbed, until well browned on the bottom, about 3 to 4 minutes. Then carefully turn balls until browned on the other side, about 2 minutes. Transfer cooked falafel to a paper towel–lined plate and season lightly with kosher or sea salt. Repeat with remaining chickpea balls.
Serve hot with Lemon-Garlic Tahini Sauce on the side, or stuffed into Homemade Pita Bread.