Trim and slice the spring onions [scallions] lengthways, so they're in strips.
In a bowl, mix together the light soy, dark soy, and black vinegar [or rice wine vinegar] and put to one side
Heat a large pot of boiling water and cook the noodles according to the packet instructions - around 5 minutes is enough usually for me.
Meanwhile, in a large wok or frying pan, add the oil and heat until very hot and smoking. Carefully add the spring onions and then stir-fry until they release their flavour and they're burnt - almost dark brown/black. Set aside, or you can transfer to a bowl.
Drain the noodles and transfer to a large mixing bowl. Add the soy sauce mixture and then the spring onion oil, and using tongs, mix the noodles thoroughly with the oil and soy sauce and vinegar.
Serve immediately.