In a small bowl, combine the first six ingredients. Pour 1/2 cup marinade into a large resealable plastic bag. Add the mushrooms; seal bag and turn to coat. Refrigerate for 15 minutes. Cover and refrigerate remaining marinade.
Drain mushrooms and discard marinade. Transfer mushrooms to a grill wok or basket. Grill, uncovered, over medium heat for 8-12 minutes or until tender, stirring frequently. Cool slightly.
Meanwhile, in a large bowl, combine the spinach, oranges, onion, almonds and grilled mushrooms. Drizzle with reserved marinade; toss to coat. Serve immediately.
Editor's Note: If you do not have a grill wok or basket, use a disposable foil pan. Poke holes in the bottom of the pan with a meat fork to allow liquid to drain.