Put the chicken quarters, onion, garlic, ginger, measurement water and salt and pepper to taste in a saucepan. Bring to the boil, then reduce the heat and simmer gently, uncovered, for 30 minutes, skimming off any scum that rises to the surface.
Remove the chicken and strain the stock. Leave to cool, and meanwhile skin the chicken and shred the flesh.
Cook the noodles in boiling water for 6 minutes. Drain well and divide between 4 bowls.
Heat the stock in a saucepan with the soy sauce. Add the chicken and simmer for 5 minutes.
Spoon the stock and chicken over the noodles and sprinkle over the chilli, spring onion slices and coriander leaves. Serve immediately.