I made this tonight, and it is delicious and super easy. I subbed dry egg noodles for fresh and napa cabbage for bok choy.
For the spicy noodle sauce, toast the sesame seeds in a dry frying pan for 2-3 minutes or until golden. Be sure to keep the seeds moving in the pan so colour evenly. Transfer to a mortar and use a pestle to grind to a semi-fine powder. Transfer to a small bowl.
Use the mortar and pestle to bruise the spring onion and garlic. Try to make sure the garlic is finely ground but leave the spring onion quite chunky. Transfer to the same bowl as the sesame seeds. Add the soy sauce, vinegar, chilli oil and sesame oil. Mix to combine.
Add the noodles and bok choy to rapidly boiling water. Cook for about 30 seconds or until just al dente. Drain and transfer to a large bowl. Add the chicken and pour over the spicy noodle sauce. Mix until well combine. Divide among serving bowls. Top with sliced cucumber.