Preheat the oven to 200C/180C Fan/Gas 6.
Peel and chop the sweet potatoes into bite-sized chunks, then place onto a baking tray. Roast for 45 minutes to 1 hours or until golden and tender.
Meanwhile, put 2 tbsp of oil in a large pan over a medium-high heat, then add the onion, peppers and garlic and cook for 5 minutes, stirring regularly or until softened and starting to caramelise.
Add the beans, juice and all. Tip in the tomatoes, breaking them up with a back of a spoon, then stir well.
Bring to the boil, then reduce the heat to medium-low and leave to tick away for 25 to 30 minutes or until thicken and reduced- keep an eye on it, and add a splash of water to loosen, if needed.
Stir the roasted sweet potato through the mix.