Rub the bell peppers and chillies with a few drops of oil and roast over an open flame on the stove, turning every few seconds to make sure that their skin is charred on all sides. Alternatively, halve the bell peppers, rub the outsides with oil, place on a lightly greased baking sheet, the cut side facing downwards and roast at 180℃ for 20 minutes till well charred. Do not cut the chillies for roasting in the oven.