1-Heat vegetable oil in a large skillet: Heat vegetable oil in a large skillet over medium high heat. Brown the chuck roast on both sides, about 3 to 4 minutes per side.
2-Transfer the browned chuck roast to the: Transfer the browned chuck roast to the slow cooker. Pour the two cans of French Onion Soup and the one can of Beef Consomme over the top. Stir to combine, then cover and cook on high for 4 hours or on low for 8 to 10 hours.
3-Carefully remove the chuck roast from the: Carefully remove the chuck roast from the slow cooker and transfer to a large bowl. Use two forks to shred the meat into thin strips, discarding any large pieces of fat.
4-Pour the juices from the slow cooker: Pour the juices from the slow cooker into a medium saucepan and bring to a simmer over medium heat. For a thicker au jus, whisk together the cornstarch and cold water, then add to the simmering broth and cook for a couple of minutes until desired consistency. For a thinner au jus, simmer to reduce by about half.
5-Pile the shredded beef onto the hoagie: Pile the shredded beef onto the hoagie rolls. Layer one or two slices of provolone cheese on top. Place open sandwiches on a baking sheet and broil on low for 2 to 3 minutes until cheese is melted, bubbly, and golden brown. Serve hot with au jus on the side for dipping.