In small bowl, mix garlic, Worcestershire sauce and pepper. Rub on both sides of beef brisket. Cut beef in half or thirds to fit slow cooker. In 3 1/2- to 6-quart slow cooker, place sliced onion. Top with beef pieces. Sprinkle with soup mix. Add water.
Cover; cook on Low heat setting 8 to 10 hours.
Remove beef from slow cooker; place on cutting board. Cut beef across grain into thin slices. Skim fat from juices in slow cooker. Return beef to slow cooker; mix well.
To serve cut rolls horizontally in half. Spoon beef mixture onto bottom halves of rolls. Drizzle with juices. Cover with top halves of rolls.