Heat a wok or a large frying pan over a high heat. Drizzle in 1/2 tbsp of the oil and stir-fry the duck for 5 mins until cooked through and golden. Set aside on a plate. Heat the remaining 1/2 tbsp oil and add the pak choi, onion, carrot and celery. Fry for another 5 mins until golden but still crunchy.
Mix the vinegar, five spice, hoisin, 6 tbsp water, and cornflour together in a small bowl. Add to the wok with the veg along with the cooked duck. Stir well and simmer for 2-3 mins until the sauce thickens and coats the veg. Scatter with the spring onions and serve with noodles or rice and the lemon wedges for squeezing over.
