1/2 cup soy sauce (light, Kikkomanns)
1/4 cup rice wine vinegar
1 tablespoon sesame oil (dark, oriental kind)
1 teaspoon grated ginger
1 teaspoon (or less) wasabe powder (green horseradish powder)
1 teaspoon sugar
If you can get hold of some sesame paste, you can add about a T of that to make for a more opaque salad dressing.
Mix ingredients well and chill.