I have made this dish several times from scratch, making my own sauce by mixing toasted sesame oil, ginger juice, soy sauce and spices. Recently I saw a bottle of Organic Soy Ginger Sauce at Whole Foods (365 Organic Everyday Value store brand) that had all the key ingredients for this dish, plus some extra spices and other things.
I cooked udon noodles, drained them and rinsed them under cold water. I mixed the noodles with Soy Ginger sauce, chopped green onions and chopped peanuts. Very good, flavorful and satisfying dinner that only took minutes to prepare :-)