Preheat oven to 200°C. Spread the diced sweet potatoes onto a baking tray and sprinkle them with 1 tbsp of paprika, salt, pepper and some olive oil. Mix it around so the potato is coated with the oil and seasoning. Put it in the oven for 20-25 minutes.
While the sweet potato is roasting, heat a large saucepan over a medium heat and add the olive oil.
Sautée the onion until soft and translucent. Add the red pepper and let it cook down for a few minutes. Add the rest of the paprika and the cumin seeds and fry for a couple of minutes, stirring continuously so you don't burn the spices.
Mix in the tomato purée, chopped tomatoes, vinegar and beans. Fill the empty chopped tomatoes tin with water and add that too. Mix everything, bring to the boil then simmer for around 30 minutes.
The sweet potatoes should be done by the time the chilli is simmering, so add these it too.
If the mixture looks a bit too thick, add a bit more water or put the lid on the pan.
Once it's at the consistency you like, it's ready to serve.