Season the flank steak liberally on both sides with coarse sea salt and fresh cracked pepper. Allow to rest on the counter for about an hour before grilling.
Preheat your grill or grill pan to medium high.
Place the flat breads on a sheet pan or platter. Divide the provolone cheese across the 4 loaves of flat bread.
Grill the steak for 4 to 5 minutes per side. Take it off the heat at 130°-140° for medium-rare or 145° for medium. Tent loosely with foil and let it rest for 7 to 10 minutes.
Meanwhile, grill the flat breads for 3 to 5 minutes until the provolone has melted and the bottoms are toasty.
Cut thin slices of steak across the grain of the meat (i.e. perpendicular to the striations). Then, cut the slices in half or into smaller bite size pieces.
Divide the arugula between the flat breads. Do the same with the steak. Finally, drizzle chimichurri sauce over each.
Cut each flat bread into wedges before servings. These can be served warm or at room temperature.