Place the duck on a roasting tray, and cook per pack instruction.
To make the pancakes, place the flour, cornflour, water, milk and butter in a food processor. Blend until smooth and leave to sit for 15 minutes.
Bring a non stick frying pan to a medium heat. Pour enough batter into the pan to thinly cover the base (like a crepe). Cook for 1-2 minutes or until the batter has set, then flip and cook for another minute. Set aside on a plate and repeat until the batter is used.
Cut or shred the Peking duck into pieces. To assemble the pancakes, spread a pancake with hoisin sauce. Lay some duck, cucumber, spring onion and peanuts in the center and roll. Serve immediately.