Cook the noodles in a saucepan of boiling water following packet directions or until tender. Drain well.
Combine the soy sauce, sugar and garlic in a small bowl. Heat the oil in a medium frying pan. Add the chicken and cook for 5 mins each side or until chicken is just cooked through. Add the soy sauce mixture to the pan. Increase the heat to high. Cook, turning the chicken, for 5 mins or until the sauce thickens and chicken is well coated. Transfer to a plate. Cover and set aside for 5 mins to rest.
Meanwhile, place the broth in a medium saucepan. Bring to the boil. Add the noodles and pak choy and cook for 3 mins or until pak choy is tender.
Divide the broth mixture between serving bowls. Top with chicken and egg. Sprinkle with sesame seeds and chilli, if using, to serve.