Put the chicken stock, gravy, ginger, garlic, soy sauce, miso, rice wine vinegar and chilli (if used) in a large pot.
Slowly bring to a simmer. Cover, then cook over a low heat for 25 minutes to infuse the flavours.
Add the spinach, edamame beans and shiitake and cook for another 10 minutes.
Meanwhile, in another pot cook the noodles according to the instructions on the packaging, then set aside. Peel the eggs and cut them in half.
Cut the spring onions into thin slices and shred the duck. Add these to the soup and cook for another 5 minutes.
Serve the soup in 4 bowls, then add noodles and scatter sesame seeds and coriander leaves on top. Serve with a dash of lime juice.