Cut the duck breasts into thin strips and place in a bowl.
Mix together the white pepper, garlic, ginger, five-spice powder and sesame oil in a small bowl.
Spray a large nonstick wok or frying pan with cooking spray and heat over a high heat. Add the duck and spices and stir-fry for about 3–4 minutes until the duck is just cooked through but still slightly pink in the centre, then add the hoisin sauce and sweet chilli sauce and cook, stirring, for 1–2 minutes until the duck is well coated with the sauce.
Transfer the duck to a warmed dish. Arrange the spring onions and cucumber in a serving bowl.
Warm the pancakes according to the packet instructions, then serve for each person to top with some of the duck, spring onions and cucumber, roll up and eat straight away with extra hoisin sauce to dip into.