This is a dish I became addicted to in Thailand, of all places... I'd never seen it here in Australia, so I learned to make it myself. It's extremely refreshing in hot weather. One way of serving the noodles is to place them over a dish of ice to keep them cool, but that's not necessary if you prefer not to. If you can't find dashi, which is a type of stock prepared with bonito flakes and seaweed, I have found that shop bought instant miso soup can do at a pinch. You might need to fiddle with the proportions of ingredients for the sauce to suit your taste. Some people like to add a little bit of sugar to the sauce as well.