Heat the oven to 375 degrees F (200 degrees C). Boil the chunks of sweet potato in water for about 10 minutes until they're tender but still holding together. Leave them to cool.
Meanwhile, to make the coleslaw, stir the vinegar and sugar together in a bowl until the sugar is dissolved. Then toss through the onions, carrot and cabbage and leave for 15 minutes.
Put the potato, cumin, garlic, coriander, lemon juice and flour into a large bowl. Season and mash until smooth.
Using a spoon (or your hands), shape the mix into about 20 balls. Place them onto an oiled baking sheet and bake for 15 minutes until the bases are golden brown, then flip and bake for 15 minutes more.