Preheat the oven to 200°C. To cook the chicken, season with salt and pepper. Heat oil in an oven proof skillet or pan over medium heat. Add the chicken and cook until the skin is golden brown and releases easily from the pan, about 5 minutes. Turn the chicken over and cook for another 4 minutes, until golden.
Transfer the skillet to the oven and roast for 15-20 minutes, until the chicken is cooked through. Remove from the oven and set aside for later.
While the chicken is roasting prepare the rest of the dish.
In a large pot, heat sesame oil over medium-low heat. Trim the ends off the spring onions and chop through the white and light green stem. Save the dark green tops for topping.
Add the spring onions to the pot with the garlic and ginger. Cook, stirring occasionally for 2-3 minutes until the garlic and ginger is fragrant. Add the mushrooms and cook for another 3-5 minutes, until the mushrooms are soft.
Add in chicken stock and soy sauce and bring to a boil, reduce to a simmer, and cook for 5 minutes.
While the broth is simmering, cut the end off the head of bok choy. Cut off the stems and cut them into thin strips. Roll the leaves together and cut them into strips.
Add the stems to the broth and cook for 5 minutes or until stems are starting to be tender. Add in the leaves and cook for another 5 minutes.
Add in the egg noodles and simmer the soup until the noodles and bok choy are tender, 8-10 minutes. Taste and add salt as needed.
Divide between two bowls. Slice the chicken breast into strips and add to the noodle bowls. Top with remaining spring onion and fresh chilli.
If you want it to be more soupy, add in an extra 2 cups of water or chicken stock.