Set steak out about an hour before grilling to allow it to come to room temperature. Light grill, turning burners on to high heat.

Pat the flank steak dry on both sides with paper towel. Season each side with a generous one-fourth teaspoon salt and several grinds of pepper.

Just before cooking, brush each side of steak with about 1 tablespoon chimichurri sauce. Grill over hot fire, cooking about 1 minute on each side, then turning the steak 90 degrees and cooking the same side an additional minute or two before flipping the steak over to give each side nice grill marks. Repeat with the other side, cooking the steak a total of 4 to 6 minutes. Remove from heat.

Rest the steak 5 minutes before slicing. Cut across the grain and on a deep bias, in wide, thin slices. Serve, passing remaining chimichurri sauce on the side.