For the gyoza skins, sift the flour into a large bowl and mix in the salt. Stir in the boiling water using a fork or a pair of chopsticks until the mixture comes together as a dough. (You many not need to use all of the water.)
Roll the dough into a ball, cover with cling film and set aside to rest for one hour.
Meanwhile, for the prawn and pork filling, mix all of the pork and prawn filling ingredients together in a large mixing bowl until well combined. Season well with salt and freshly ground black pepper. Chill in the fridge until needed.
For the gyoza skin (buying is so much easier), turn out the dough onto a lightly floured surface and knead for five minutes until smooth.
Cut the dough into three equally sized pieces and roll each into a ball. Roll out one of the balls onto a lightly floured work surface, stretching and turning the dough as you go, until the gyoza dough is as thin as possible.
Using a 10cm/4in cookie cutter, cut discs from the gyoza dough and repeat the rolling and cutting process until all of the dough has been used.
To assemble the dumplings, hold a gyoza skin in the palm of your hand and add one teaspoon of the filling mixture. Wet the edges with a little water using your fingertip and seal the dumpling, pinching along the edges to create a pleated fan effect (the end result should resemble a mini Cornish pasty).
Repeat the process until all of the filling mixture and gyoza skins have been used up, setting each dumpling aside on a plate dusted with flour.
To cook the dumplings, heat the vegetable oil in a large frying pan with a lid over a high heat. Arrange the gyoza in the pan, leaving space between each one, and fry for 2-3 minutes, or until the bottoms are golden-brown.
Add 100ml/3½fl oz of water to the pan, cover with the lid and steam the dumplings for a couple of minutes.
Give the pan a shake to release the gyoza from the bottom of the pan and continue to cook for a further two minutes with the lid off, until the filling is completely cooked through.
Serve the gyoza immediately with a dipping sauce such as a mix of soy and lime juice.