Cook the udon noodles as per the instructions. Strain them.
Heat the sesame oil in the pan and briefly fry the Peking cabbage so that it softens and takes on a little colour.
Move the cabbage to one side of the pan, add a little more sesame oil, and then the prawns. Cook them for a minute, turning half-way through.
Add half of the soy sauce, mix in and let it simmer. Then add the udon noodles and mix in.
Add the rest of the soy sauce, the oyster sauce, and the sriracha sauce to taste. Mix this all together thoroughly and let it bubble away for 2 minutes.
Turn off the hob and add most of the spring onions, setting some aside as garnish. Mix this together and get ready to plate up.
Serve in a bowl with a scattering of spring onions and a sprinkle of sesame seeds.