Cut the peppers into bite-sized pieces and put into a roasting dish along with the red onion slices, sweet potato, spring onion, cumin, coriander, olive oil, a sprinkle of salt and a good grind of black pepper.
Mix through with your hands, breaking up the red onion pieces until the spices are well combined and all the vegetables are coated in the oil.
Cover with foil and bake for 20 minutes.
Remove the foil and give it a good stir, then roast for a further 20 minutes or until golden and sweet.
Serve with plain yoghurt stirred through with chopped mint and a little salt and a nice piece of grilled chicken or fish.