Coat the prawns in the soy sauce and mix in the cornflour.
Put the oil in a pan, not too hot. Add the spring onions and start to cook. Add the coated prawns after 1 minute.
Mix the soup 'goo' ingredients to make a thick paste, then add to the pan. After a minute, add the water gradually until you have a soup consistency that suits you (bearing in mind that you'll be adding noodles and beansprouts shortly).
Add the beansprouts and noodles and cook for a couple of minutes until the beansprouts are cooked but still slightly crunchy.
Serve with hunks of bread to soak up the garlicky, spicy liquid and to mop up the bowl!