In a small bowl, combine the potato starch and 30ml water and set aside.
In a large wok, heat the vegetable oil over a medium-high heat. Add the pork and cook for 6-7 minutes, stirring frequently, until browned on all sides, then add onion, garlic, ginger and radish and cook for 5 minutes, until onions have softened.
Stir in black beans, sugar, salt and pepper to taste. Add soy and chicken stock. Simmer gently for a minute or two. Stir in potato starch mixture, simmer for a further 3 minutes, stirring frequently until sauce thickens.
In a large pot of boiling salted water cook the noodles according to instructions, drain and rinse. Divide the noodles into 4 big bowls. Spoon the pork and sauce mixture on top of noodles and garnish with cucumber, sesame oil and sesame seeds. (Note: Potato starch, pickled radish and salted black beans are available from Asian food stores.)