Heat oven to 450°F. Make pie crusts as directed on box for Two-Crust Pie, using 9-inch glass pie plate. In 12-inch skillet, cook beef, onion, garlic salt and pepper over medium-high heat, stirring occasionally, until beef is thoroughly cooked; drain.
Stir cornstarch into beef mixture until mixed. Stir in potatoes, carrots and gravy. Cook 5 to 6 minutes over medium-high heat, stirring constantly, until hot. Spoon into crust-lined pie plate. Top with second crust; seal edge and flute. Cut slits in several places in top crust; cover edge of crust with foil.
Bake 35 to 40 minutes or until crust is golden brown. Let stand 5 minutes before serving.