Method. 1  Rub each potato with a little oil and salt, then wrap in a double layer of foil. 2  As soon as the barbecue coals are glowing red, put the potatoes directly on them. 3  Peel back the top of the foil from each potato, split open and top with a spoonful of yogurt and a few spring onion slices.ethod. 1  Rub each potato with a little oil and salt, then wrap in a double layer of foil. 2  As soon as the barbecue coals are glowing red, put the potatoes directly on them. 3  Cook for 15 mins, turn with tongs, then cook for 15 mins more. 4  Remove one, unwrap and check it is cooked through.