Slice beef into very thin strips.
Spray skillet with cooking spray and heat over medium-high heat 1 minute. Add beef and cook until browned, stirring often. Remove beef.
Remove skillet from heat. Spray with cooking spray. Add broccoli, mushrooms, onion and garlic powder and cook until tender-crisp.
Add soup, water and soy sauce. Heat to a boil. Return beef to skillet and heat through. Serve over rice.
Tip: To make slicing easier, freeze beef 1 hour.