First prepare the broth. I prefer a chicken broth powder, in which you add water, as the flavor is very light. If you cannot find these I suggest buying straight chicken broth and diluting it with some water. Bring the broth to a boil and add the onion. Let the onion soften, then reduce broth to low temperature to keep warm. Cook the noodles and set aside. Marinate the tofu after cubing in soy sauce (I prefer kikoman brand as it's much less salty and more flavorful than most, but you can use whatever you chose). Let tofu sit for 5 minutes. Sautee until a little colored and crisp. Add tofu to the broth, some of the soy will be pulled out of the tofu to add a more asiany flavor to the broth. The rest is just add to preferred taste. Pour broth into a serving bowl about half full, add bean sprouts, plenty of noodles, several pinches of cilantro and green onion sprinkled on top. I prefer it very herby as it has an extremely fresh taste, but just sprinkle to your liking. If desired squeeze some fresh lime into the soup. Makes extremely good fresh left overs as well. Store broth separate from noodles, bean sprouts, and herbs.