Drain and rinse the soaked chickpeas, then add them to the bowl of a food processor. Add the onion, garlic, parsley, dill, spices, baking powder, and tahini to the bowl as well. Process on high, scraping down the sides of the bowl as necessary, until the ingredients are well-combined and the mixture resembles coarse sand. Shape the falafel into approximately 15 round balls about the size of a golf ball.
¼ large yellow onion, 2 cloves garlic, ¼ cup parsley, 1 tablespoon dill, 1 teaspoon cumin, ½ teaspoon kosher salt, ⅛ teaspoon black pepper, ½ teaspoon baking powder, ½ tablespoon tahini