Mix vinaigrette dressing ingredients together with a whisk or by shaking in a closed Mason jar. Set aside.
Cut the asparagus into two or three inch pieces and steam in a vegetable steamer, or place in a shallow pan of water, and cook until the spears start turning dark green. You want them tender-crisp, so don't over cook.
Drain the asparagus and run under cold water (or submerge in an ice bath) to stop the cooking process and to chill the spears.
Sprinkle with crumbled feta, if using.