Make the chimichurri: In a bowl, combine parsley, oregano, garlic, shallot, red pepper flakes, 1 tsp salt, and ½ tsp pepper. Add vinegar and stir. Let sit 5 minutes, then whisk in olive oil in a slow stream. Set aside at room temperature.

Prepare the steak: Pat the steak dry with paper towels. Season generously with salt and pepper on all sides. Let sit at room temperature for 20 minutes.

Set up the grill for two-zone cooking: For charcoal, bank hot coals to one side. For gas, turn half the burners to high, leave the other half off. Target 450–500°F on the hot side.

Sear the steak over high heat: Place steak on the hot side. Cook 3–4 minutes per side for a good crust. Do not move it during each side.

Move to indirect heat: Transfer steak to the cooler side. Close the lid. Cook until internal temperature reaches 125°F for medium-rare (about 4–6 minutes, depending on thickness). Use an instant-read thermometer inserted into the thickest part.

Rest the steak: Remove from grill. Place on a cutting board. Spoon 2 tablespoons of chimichurri over the top. Let rest 8 minutes. Do not skip this — resting reabsorbs juices.

Slice and serve: Slice against the grain into ½-inch strips. Drizzle with remaining chimichurri. Serve immediately.