Place roast in a 3- to 4-qt. slow cooker; top with onion. Combine the broth, water, chipotle peppers, adobo sauce, gravy mix, Creole seasoning, chili powder and cumin; pour over meat. Cover and cook on low until meat is tender, 8-10 hours., Remove roast; cool slightly. Skim fat from cooking juices. Shred beef with 2 forks and return to slow cooker; heat through. Using a slotted spoon, place meat on rolls. Serve with guacamole or salsa if desired and the cooking juices. Freeze option: Freeze individual portions of cooled meat mixture and juices in freezer containers. To use, partially thaw in refrigerator overnight. Heat through in a saucepan, stirring occasionally. Serve on rolls, with guacamole and salsa if desired.