Heat the oil in a large saucepan and add the onion, chilli and garlic and cook without colouring for 1-2 mins. Tip in the sweet potato, spices and some seasoning, then pour in the beans and chopped tomatoes. Fill one of the empty cans with water and add to the pan, then bring to the boil and turn down to a simmer.
Cook for 45-50 mins or until the sweet potato is soft and the sauce has reduced – add some water if the sauce looks a bit thick. Stir through the lime juice, season to taste and serve with cauliflower rice.