Put all the chicken ingredients, apart from the chicken, in a large pan with 1 litre water. Bring to the boil, add the chicken, then simmer for 20-25 minutes or until the chicken is cooked. The meat should come off the bone with little effort. Lift the chicken onto a plate and leave to cool, then shred into strips. Discard the skin, bones and cooking liquid.
Mix the marinade ingredients in a medium mixing bowl, add the shredded chicken and marinate for 1 hour or longer.
Mix the sesame paste ingredients in a small mixing bowl and set aside.
Soak and cook the noodles according to the packet instructions, run under cold water for 2-3 minutes to remove the starch, then keep chilled until ready to serve. To assemble the ban mein, put the cold noodles in a bowl or on a platter and arrange the marinated chicken on top. Spoon over some of the sesame paste followed by the beansprouts and cucumber in a mound in the middle of the bowl. Sprinkle the peanuts around the outside, spoon over as much of the chilli oil as you want, then decorate with the coriander leaves, sliced chilli and sesame seeds. Serve cold.