Preheat the oven to 200c. Make the dressing: mix all the liquid ingredients together, then add the sliced garlic and grated ginger. Lightly score the duck fat and spoon one-third of the dressing over the duck.
Place a dry flameproof baking dish on the hob over a medium heat and seal the duck breast, fat side first, then place the baking dish in the oven and cook for 8 minutes. Remove from the oven and allow to cool. Keep the oven on. Once the duck is cool enough to handle, slice each breast into thin slices and then toss the slices in 2 more tablespoons of the teriyaki dressing. Return to the oven for a further 2 minutes to allow the dressing to caramelise slightly. Soak the noodles as per the instructions on the packet. Boil a pan of water and blanch the beans for 1 minute. Drain and add to the cooked noodles, mix in the coriander sprigs, shallots and spring onions. Add the slices of duck with the remaining dressing and mix well. Garnish with more coriander and serve.