Snap off tough ends of asparagus; remove scales from stalks with a knife or vegetable peeler. Cut asparagus diagonally into 1 1/2-inch pieces; set aside.
Heat 1/4 cup oil in a wok or heavy skillet. Add asparagus pieces, onion slices, salt, pepper, and orégano; stir well. Cover and cook 8 minutes or until vegetables are crisp-tender. Drain before serving.