Place spinach and red pepper on large serving platter or divide evenly among 4 individual salad plates. Set aside. In a large skillet, heat 1 tablespoon oil over medium-high heat. Saute steak quickly until medium rare. Remove from pan. Add remaining oil and saute onion slices until softened and translucent. Stir in vinegar, water, honey, mustard, ginger, salt and pepper. Bring to a boil. Quickly stir in meat. Spoon over spinach. Serve immediately.