Place the flank steak on your cutting board and season it with some salt. Put a tablespoonful of the mushroom and onion mix on top, then spread it evenly across the steak.
Sprinkle the spinach on top of the steak, then the provolone slices. Make sure you press down lightly to compress the spinach.
Starting at the bottom of the steak, roll it up tightly. Secure the steak roll into place using toothpicks (you’d probably need around six).
Slice the steak roll into six equal rolls. When you’re done, Heat the remaining oil in the pan over high heat. Sear the steak rolls on one side for about one to two minutes, and then flip them.
Sear the second side of the steak rolls for about a minute. After searing the steak, bake it for 10–15 minutes.
Take out the toothpicks, then serve. Enjoy!