Combine and thoroughly mix all ingredients for vinaigrette in a small bowl, and set aside.
Prepare the asparagus by snapping off the ends and removing the tops. Using a vegetable peeler, shave asparagus and cucumber into thin strips. This is best done while laying the vegetable on a flat surface and pushing in and away from the body, peeling back to front.
When veggies are shaved, mix them together in a medium bowl, then pour over and mix in the vinaigrette.
Serve cold and garnish with green onion and chili flakes.