Lay a chicken breast between 2 sheets of clingfilm and flatten with a rolling pin or meat mallet until it is 2.5 cm (1 inch) thick. Repeat with the remaining chicken breasts. Transfer to a baking sheet and brush with some of the hoisin sauce.
Cook the chicken breasts under a preheated hot grill for 4 minutes. Turn them over, brush with the remaining hoisin sauce and cook for a further 3 minutes or until the chicken is cooked through.
Meanwhile, warm the pancakes in a bamboo steamer for 3 minutes or until heated through.
Slice the chicken thinly and arrange it on a serving plate. Serve with the pancakes, accompanied by the cucumber, spring onions, coriander and diluted hoisin sauce in separate bowls, so that everyone can assemble their own pancakes.