1) Boil the sweet potato for 10--15 minutes until soft. Drain well, mash and leave to cool for 30 minutes.
2) Meanwhile, heat half the olive oil in a small pan. Add the garlic and cook for 5 minutes until softened. Add the garlic and chilli pepper and cook for another couple of minutes.
3) Mash the chickpeas in a large bowl and stir in the onion mixture. Add the sweet potatoes and spices and combine.
4) Line and grease a baking sheet with the remaining olive oil. With your hands form the mixture into around 10 burgers and place them on the baking sheet. Bake in the oven at 180°C for 15 minutes. Carefully turn them over and then bake for another 15 minutes. Serves 3 to 4.