Place beef into the slow cooker. Add Italian salad dressing mix, water and if you want the extra kick of heat, add the optional red pepper flakes.
Cook on low setting 6-8 hours.
About 15 minutes before serving, stir in pepper rings. If using a chuck roast, pull apart with fork when fully cooked. Add pepper rings and let meat roast in juices for 30 minutes to one hour.
Toast sandwich buns under broiler and then serve with a generous amount of Italian beef.