Make the homemade french onion soup mix by mixing the dried onion, onion powder, celery seed powder, ground pepper, ½ teaspoon of salt, and oregano.
Rub the dry mixture all over the chuck roast and place the beef into the slow cooker insert.
Whisk together the Worcestershire sauce and beef broth then pour into the slow cooker insert.
Place the lid on and then set it to cook for 8-10 on low or 5-6 hours on high. The beef should be very pull apart, fork-tender, and shred easily when done.
Remove the beef and place it into a bowl. Using two forks, shred the beef. Mix in some of the juices from the slow cooker and stir in the rest of the salt. Start with 1/2 teaspoon of salt and add in the rest if you need to.