Season beef with garlic powder, salt and pepper and place in slow cooker. Mix together broth and cornstarch and pour on top of beef. Add onion, red and green pepper and bamboo shoots. Pour in stewed tomatoes and soy sauce. Mix well.
Cover and cook on high for 3-4 hours or low for 6-8 hours. Stir before serving over rice, egg noodles or chow mein.