Start by butterflying your flank steak and pounding it out with a meat tenderizer until the entire thing is about 1/2” thick.
Combine the kosher salt, coarse black pepper, and granulated garlic in a small bowl and season the steak with this mixture.
Using a spatula or butter knife, spread the Boursin cheese over the top of the butterflied flank steak.
Add a layer of shredded parmesan, then a layer of baby spinach, then finish with a layer of shredded mozzarella cheese.
Using your hands, roll the flank steak up tightly into a cylindrical shape.
Secure the steak with butcher’s twice every 1-1/2” to 2” and tie tightly.
Let the rolled up flank steak rest in the freezer for about 15 minutes.
Preheat your grill to 400°F.
After the steak has chilled in the freezer for 15 minutes, remove it and grab a sharp knife. Slice the steak into pinwheels between the butcher’s twine. Leave the twine intact.
Place the pinwheels directly on the grates of your grill and let them cook for 5 to 7 minutes per side, or until the steak reaches an internal temperature of 135°F.
Remove from the grill and let rest for 10 minutes, then serve and enjoy!