Pound steak to 1/4-inch thick. Cut into 1/4-inch wide strips. Melt butter or margarine in large skillet, and brown meat until all pink is gone. Add garlic and beef broth; cover and simmer for 30 minutes. Stir in onions and green peppers. Cover and cook for 5 minutes. Blend cornstarch, water, and soy sauce, and stir into meat mixture. Cook, stirring, until clear and thickened about 2 minutes. Add tomatoes and heat until they are hot through. Serve over rice.