Mix the fresh spinach, green onion, water chestnuts, and Monterey Jack cheese. Set aside.
Mix the brown sugar, chicken broth, vinegar, and hot pepper sauce in a small saucepan. Stir well. Bring to a boil, and remove from the heat; stir in the mandarin orange slices. Pour the mandarin mixture over the spinach mixture, and toss gently, and serve immediately.