In a food processor with the motor running, drop the garlic cloves through the feed tube to chop. Add the green onions and process to chop. Add the sweet potato, beet and chickpeas, and pulse until very finely chopped, about 15-20 pulses. Transfer to a bowl, and add the lemon juice, cumin, and coriander. Season generously with salt and pepper. Fold in the egg, followed by the chickpea flour. Form the mixture into 4 half-inch thick patties.