Thinly slice the onion.
Peel then grate the beetroot and sweet potato, using a course cheese grater.
Mix them with the onion, add some salt and put the mixture in a sieve. Rest for 10 minutes, then squeeze out any excess liquid.
Put the mixture in a bowl, add the grated ginger & garlic. Add the turmeric, chilli powder and chickpea flour. Combine well.
Heat some vegetable oil in a wok or deep frying pan. Add dollops of the mixture, and flatten them slightly with the base of the spoon. Fry them for about 2 minutes, then turn them over and cook until golden and crispy.
Serve at room temperature.