Cook rice noodles according to package directions. Once cooked, rinse thoroughly under cold water until cooled. Drain well.
In a small bowl, whisk together the soy sauce, sugar, rice wine vinegar, and sesame oil until the sugar is dissolved.
Add the cooled noodles, sliced cucumber, and green onions to a large bowl. Pour the dressing over the noodles and toss until evenly coated.
For the best flavor, cover and refrigerate for at least 1 hour to allow the flavors to blend and the noodles to absorb the dressing.
Before serving, toss with sesame seeds and finish with chili oil to taste.
