Toss the asparagus in 2 Tbsp of sesame oil, spread out on a baking sheet, and sprinkle with salt. Roast for about 15 minutes, or until just tender and lightly browned in places.
Put the wasabi into a screw-top jar, add the warm water, and mix into a paste.
Add the rice vinegar, olive oil, the remaining 2 Tbsp of sesame oil, and some salt, put the lid on, and shake vigorously for a few seconds until smooth.
Arrange the asparagus on individual plates, and drizzle the vinaigrette on top. Sprinkle with sesame seeds. Serve hot or at room temperature.