Using the saute function of your slow cooker or in a separate pan, sear meat in cooking fat of choice a few minutes on each side to form a crust.
Turn the slow cooker to low. If you used a separate pan, transfer meat to slow cooker. Add in the season blend and broth.
Let cook on low for 10 hours. Flip meat at some point during the cooking process to cook both sides evenly.
Remove the meat and shred with a fork.
Make sandwiches with rolls, melted cheese, the meat, and top with pickled red onions and leftover broth as your Au jus sauce. Serve some extra Au Jus on the side for dipping.