1) Heat half the oil in a large sauce pan over medium heat.
2) Add half the ginger and half the spring onions. Cook for 2 minutes.
3) Add the miso and sweet potato and stir to combine.
4) Add the water and chicken broth and bring increase heat and bring to the boil.
5) Cook for about 10 minutes, or until the sweet potato is cooked.
6) Remove from the heat and season with salt and pepper.
7) Using a handheld stick blender or a regular blender, blend until smooth.
8) While the soup is cooking, place the prawns in a bowl with the other half of the ginger and sesame oil and all of the sesame and onion seeds.
9) Cook in a large skillet over high heat for about 3 minutes. Over cooking your prawns will make them rubbery.
10) Place the soup into warm bowls and top with the prawns and the remaining green onions