Bring a kettle of water to the boil. Measure out 250 ml, pour into a small saucepan and crumble 1/2 the stock cube into it. Cook the soba noodles in the fish stock.
Meanwhile, heat the oil over a medium high heat in a saute pan.
Stir fry the sliced peppers (I used red, yellow and orange), the broccoli, ginger and garlic until the peppers begin to soften but they still retain some texture, about 3-4 minutes.
Add the noodles and the fish stock to the saute pan along with half of the spring onion. Flake in the salmon and bring to the boil so that the stock evaporates and the fish heats up.
Transfer to a serving dish and garnish with the remaining spring onion and the finely sliced red chilli, if desired.