Preheat the oven to 220 C / Gas 6. Prick the potatoes all over with a fork. Place onto a baking tray and drizzle with oil to coat. Bake for 1-1 1/2 hrs, or until cooked all the way through. Test with a fork to make sure, nothing worse than a hard baked potato.
Once they are done, slice them open. Add grated cheese, corned beef and top with beans.