Rinse chicken inside and out.
Place spring onions, the coriander roots, ginger, peppercorns, salt and the cold water in a saucepan and bring it to the boil.
Add chicken and more water if necessary, so it's submerged. Return to the boil. Cover the pan with a lid and turn off the heat. Stand chicken in poaching liquid for 2 hours.
For the sauce stir tahini, soy sauce, hoisin sauce, honey, chilli oil, the warm water and remaining sesame oil together in a small bowl until smooth.
After 2 hours, pull legs and breast meat from the chicken. Shred meat using two forks or your fingers and transfer to a large bowl. Stained poaching liquid can be frozen for up to 1 month.
Cover bean noodles with boiling water and stand for 10 minutes. Drain well, then return noodles to bowl with 1 tsp of the sesame oil.
Arrange noodles with chicken and some coriander. Top with sesame seeds and drizzle with tahini sauce.