Just before serving, remove beef and vegetables from slow cooker; place on serving platter and cover to keep warm. In medium saucepan, combine cornstarch, 3 tablespoons water and remaining 2 tablespoons horseradish; blend well. Pour juices from slow cooker into cornstarch mixture; mix well. Bring to a boil over medium-high heat, stirring constantly. Cut beef into slices. Serve beef with vegetables and gravy.