Fill a bowl halfway with ice and enough water to cover ice.
In a pot over medium heat, bring lightly salted water to a boil. Add asparagus and cook for about 20 to 30 seconds or until half-done.
With a slotted spoon, remove asparagus from the poaching liquid. Reserve about 1 cup of poaching liquid and allow to cool.
Plunge asparagus into the bowl of iced water until cold. Drain very well.
In a bowl, combine reserved poaching liquid, soy sauce, and cornstarch. Stir until blended.
In a wok or skillet over medium-high heat, heat oil until shimmering. Add onions, garlic, and ginger and cook, stirring regularly, until softened.
Add asparagus and cook for about 2 to 3 minutes or until tender-crisp.
Add liquid mixture and cook, stirring gently to combine, for about 30 to 40 seconds or until sauce is thickened.
Add cashews and stir to combine.
Serve hot over brown rice.