Preheat the oven to 250°C/230°C Fan/gas mark 9/450°F and cover a smallish baking sheet with foil.Remove the core, seeds and white membrane from the peppers then cut the peppers into strips and place on the prepared baking sheet shiny-side down. Sprinkle with the oil and smoosh them about so that all sides are a little covered by oil, then leave them, shiny-skin-side up this time. Roast them in the oven for 25 minutes.Pour 1 litre freshly boiled water into a pan, adding the vegetable bouillon powder or chicken stock cube or concentrate to make up to the required strength. Add the frozen corn niblets, bring back to the boil, reduce the heat, cover and let bubble for about 20 minutes.Using a slotted spoon, remove about a cupful of corn, and set to one side while you blend the rest of the corn along with all its cooking liquid and the blistered peppers, then toss the set-aside corn niblets back into the blended, but not too smooth, soup, and season to taste.