Wash the spring onions and chop them. Also, wash and slice shiitake mushrooms.
If you are using frozen cooked prawns put them in warm water to defrost.
Put organic miso paste in a small bowl and add a little water. Whisk it until the miso paste dissolves in water.
Heat the rapeseed oil on medium-high heat in a medium, tall saucepan. Once hot add half of the chopped spring onions. Gently fry for about half of a minute, then add sliced shiitake mushrooms.
Cover the saucepan and let the mushrooms cook for a few minutes to release their water. After a few minutes uncover the lid, stir and cover the lid again. Shiitake mushrooms are quite meaty and require longer cooking than normal mushrooms so let them cook in their water for at least 5 minutes. If required, add a little water so they don't stick to the pan.
Once shiitake mushrooms have softened, add the miso paste which you have dissolved in a little water. Also add ginger, seaweed, the rest of the spring onions and prawns.
Add additional water to make the soup more watery (but not too watery!). Leave it to cook on a small heat for a minute or so and it's done!
Once served drizzle with tamari soy sauce, according to taste.