Combine beef, brown sugar, 2 tablespoons soy sauce and garlic in plastic food-storage bag; seal; turn to coat meat. Let stand briefly.
Meanwhile, place broccoli and 2 teaspoons water in microwavable plate. Cover tightly with plastic wrap. Microwave on high for 2 minutes.
Stir together green onions, remaining soy sauce, the orange juice, cornstarch, rice-wine vinegar, ginger and red-pepper flakes in a small bowl.
Heat peanut oil in wok or large skillet over high heat. Add beef with marinade; stir-fry 1 to 3 minutes. Add broccoli; stir-fry 1 to 2 minutes or until heated through. Add cashews; cook 1 minute. Stir in green onion-orange juice mixture; cook 2 to 3 minutes or until thickened.
Serve immediately with instant brown rice and garnish with thin strips lemon rind if desired.