Season both sides of chuck roast with salt, pepper, garlic powder and oregano.

Press the SAUTE button on the Instant Pot. Add the olive to to the inner pot and heat to hot. Add the chuck roast to the pot and brown for 4-5 minutes per side. 

Remove chuck roast from the pot and place rack into post. Pour in beef stock and place browned roast on the rack. Place lid on top and lock. 

Set top valve to Sealing. Press the Meat button and set for 60 minutes. 

When the timer is done, let naturally release for ten minutes, then quick release. Remove lid and lift out rack. Transfer meat to cutting board and shred. 

Turn the Instant Pot to Sauté. Sprinkle the flour over the remaining beef stock. Whisk vigorously until flour is completely incorporated. Bring to a simmer until slightly thickened.

Preheat oven to 350 F. If desired, spread a sub roll with garlic bread spread. Pile bun with shredded beef. Top with 4 half slices of provolone. Transfer to a baking sheet and repeat with remaining buns. 

Bake for 6-8 minutes, until bun is toasted and cheese is melted. Serve with hot au jus for dipping.