Rub the duck with olive oil. Sprinkle with salt and pepper, then the five spice. Put in a high sided roasting dish and cook for 1 hour 30 minutes.
Remove from the oven, put on a plate and cover with foil. Rest for 45 minutes.
Meanwhile, peel your potatoes. Cut into chip shapes and put in a saucepan full of cold water. Parboil for 20 minutes, then drain and leave to dry. When you remove the duck from the oven, tip the chips into the roasting dish that you cooked the duck in and put in the oven (increase the temperature to 220 degrees Celsius) for 45 minutes.
To make your sauce, put the soy sauce, peanut butter, rice vinegar, sesame oil and garlic powder into a jug. Whizz with a stick blender until thick and smooth.
To serve, cut the cucumber into wedges. Give everyone a portion of cucumber, duck and chips and serve with a spoonful of hoisin sauce on the side.