01 - Pat beef chuck roast dry with paper towels, then season evenly with black pepper on all sides.
02 - Place roast in the center of slow cooker. Sprinkle onion soup mix over beef, then add condensed cream of mushroom soup, beef broth, and Worcestershire sauce. Stir liquids gently to combine around the beef.
03 - Cover and cook on LOW for 8–10 hours or HIGH for 4–5 hours until beef is fork-tender and easily shreds.
04 - Remove cooked beef to a cutting board and shred with two forks. Return shredded beef to the slow cooker, mixing well with the gravy.
05 - Toast sandwich bread slices on a baking sheet in a preheated oven at 190°C (375°F) for 5 minutes or until golden, if desired.
06 - Lay each toasted bread slice on a plate, top with a scoop of hot mashed potatoes, then ladle generous portions of shredded beef and gravy over the top.
07 - Finish with a sprinkle of chopped fresh parsley if desired, and serve immediately while hot.