01 -
In a large skillet over medium heat, cook the ground beef and sliced onions together, breaking up the beef as it cooks until no pink remains.
02 -
Drain off any excess grease from the cooked beef and onion mixture to prevent your sandwiches from being too greasy.
03 -
Add the drained beef mixture to your slow cooker, spreading it out evenly across the bottom.
04 -
Stir in the quick oats, beef broth, onion soup mix, Worcestershire sauce, garlic powder, and black pepper until everything is well combined.
05 -
Cover and cook on low heat for 3-4 hours, allowing all the flavors to meld together and the mixture to thicken.
06 -
About 15-20 minutes before serving, lay the provolone cheese slices over the top of the beef mixture and cover again to let it melt.
07 -
While the cheese melts, lightly toast your brioche buns if desired. This helps prevent them from getting soggy.
08 -
Spoon the cheesy beef mixture generously onto the bottom halves of your buns, then top with the other half. Serve with small bowls of the cooking liquid for dipping.