Grease the inside of a slow cooker with non-stick cooking spray.
Separate the deli beef slices, spreading them out so they aren’t stuck together and layering them all at the bottom of the slow cooker.
Pour the jar of beef gravy over the beef slices.
Using tongs, toss the beef slices until each one is completely coated with the gravy.
Cover the slow cooker with its lid and cook on LOW for 2 hours, or until the meat is hot throughout and bubbling slightly.
About 10 minutes before you’re ready to serve, slice the hoagie rolls in half and toast them in the oven at 400°F for 3-5 minutes, until they are golden and crisp.
Once the beef is done cooking, use tongs to load the beef and gravy onto the toasted buns.
Top with a slice of provolone cheese, letting the residual heat from the beef melt it slightly.
Serve warm!