Mix up the sauce. First mix the warm water and peanut butter into a smooth paste. Next, add the rest of the ingredients, except the garlic and scallion, and stir the mixture into a very smooth sauce. Its best to add the garlic and scallion just before serving, but in these hurried times its OK to mix everything together when you have time, up to a day before. The sauce keeps a while if refrigerated.
The sauce is intended to be served separately with cold noodles and mixed together by each person (I haven't actually done this for years), but for parties its better to mix the noodles with sauce before serving. It takes a while to mix the thick sauce into the big nest of noodles. Sometimes I cut the noodles after cooking to make it easier to mix them with sauce. If the sauce is too thick to mix, mix in extra water first.
Noodles: I use about 1.5 lbs of thin egg noodles for the above recipe. This is a lot of noodles to cook at the same time. Preparing the noodles the night before is a good idea. Cook, rinse with cold water, drain and refrigerate them in plastic bags. The best noodles are thin chinese egg noodles, either plain or flavored (chicken or shrimp). These come in cellophane as coils of dried thin noodles, usually 15 0z/pkg in Chinese grocery stores. Fresh noodles are also very good if they're relatively thin - Japanese, buckwheat, Italian- any noodle will do if its not too thick.
^*SAN-J brand makes one low salt soy sauce, "reduced sodium TAMARI soy sauce".
^#Note: the original recipe called for 8 tsp. cayenne (not recommended for the faint of heart!! For the hearty, use 10-14 small dried Chinese or Thai chiles ground to dust in a coffee grinder)