Put the sweet potato slices onto a baking tray and coat in the oil, salt and pepper. Place in a pre-heated oven on medium heat for 45 minutes, turning occasionally.
Char-grill the peppers on a griddle pan (high heat) for approx 15 minutes, turning frequently until nice and charred on both sides. Set aside and when they are cool, chop finely.
Pop the tomatoes in a large bowl and pour over boiling water, when the skin begins to spilt remove from the water and peel off the skin. Remove the seeds and juice from inside the tomatoes and then cut into quarters. Set aside.
Pour the olive oil into the pan and add the spring onion, garlic and cumin. Fry on a medium heat until just colouring and get soft. Add the tomatoes, peppers, chilli flakes, salt and pepper. Simmer for 15-20 minutes until soft. Note, you may need to keep adding a little water if the mix is getting too dry.
Some other things I like to add in if I have them to hand; a handful sun-dried or sun blush tomatoes, olives, capers, more chilli, kale.
Place the sweet potato slices on top to serve and dollop in some cashew cheese. Great with chucks of bread and salad.