Using sharp knife, lightly score the steak about 1/8 inch deep on both sides in a crisscross pattern at 1/2-inch intervals.
In a small bowl combine the cumin, garlic powder, oregano, freshly ground pepper and kosher salt. Season both sides of the steak with season spices.
For the chimichurri, mix all ingredients together. (Note: this tastes best when you chop everything by hand rather than in a food processor)
Prepare the grill on high heat. Grill the steaks to desired doneness, about 3 to 4 minutes per side for medium-rare, turning steaks 1/4 turn after 1 1/2 minutes to form crisscross grill marks, if desired.
Transfer steaks to cutting board; let rest 5 minutes. Thinly slice steaks across grain.
Transfer to platter and top with chimichurri sauce.
Notes
You can also make the chimichurri with half cilantro, half parsley although that won't be authentic.*omit the onion and add 2 more garlic cloves