1. Stir the cornstarch, black pepper, broth, soy sauce, brown sugar and garlic powder in a medium bowl until the mixture is smooth.
2. Cook the beef in a 10-inch nonstick skillet over medium-high heat until it's browned, stirring often. Pour off any fat.
3. Add the asparagus, mushrooms and pepper to the skillet. Reduce the heat to medium. Stir the cornstarch mixture in the skillet. Cook and stir until the mixture boils and thickens. Serve the beef mixture over the rice.
Helper: For easier slicing, freeze the beef for 1 hour before slicing.