To cook the noodles, plunge them into a pan of boiling water.
Cook the noddles for four minutes and then drain and refresh in a bowl of iced cold water. Drain again.
Put the dashi stock into a saucepan and add the mirin, soy sauce and tofu. Add the sliced spring onions and wakame seaweed. Simmer for 3-4 minutes. Stir in the pack choi and allow to wilt for 1-2 minutes.
Preheat a griddle pan. Brush the salmon with oil and dust with the Japanese seven-spice powder.
Grill the salmon skin-side down on the griddle pan for 2-3 minutes, before turning over and finishing for a further 1-2 minutes.
To serve warm the udon noodles in the miso broth and ladle into serving bowls. Spoon the hot broth over.
Top with the griddled salmon and garnish with the strips of mouli and coriander leaf to serve.