In a medium bowl, cover the chickpeas and fava beans with cool water by 3 inches / 7.5 cm. Soak them overnight and up to 24 hours. Thoroughly drain the chickpeas and fava beans. In the food processor, process them with a teaspoon of salt until they are ground to a coarse crumb.

Add the mint, parsley, cilantro, jalapeño, garlic, onion, and sesame seeds and pulse until the mixture is finely ground to a moist crumb. Transfer the mixture to a bowl, stir in the baking soda, and chill for at least 30 minutes or up to 1 day.

Heat the oil to 375F / 190C in a 3-quart / 3 L saucepan or sauté pan until a dropped pinch of herb bubbles dramatically. 

Using an ice cream scoop or a large spoon, pack the falafel mixture tightly into the scoop to form 2-inch / 5 cm ovals, and fry a few at a time until they are golden brown, flipping them over with tongs as soon as they are browned on one side. 

Remove the falafel from the oil with the tongs to a paper towel-lined plate, and fry the remaining falafel. 

Serve the falafel hot with the tahini sauce on the side.