Make the sauce
Combine the cilantro, parsley, oregano, and garlic in a food processor and pulse until finely chopped. Scrape the mixture into a bowl and stir in the olive oil, vinegar, lime juice, red pepper flakes, and 1/2 tsp. salt.
Cook the steak
In a flat dish or shallow bowl, combine the crushed peppercorns with 2 tsp. salt. Firmly press both sides of the steaks into the mixture so they’re well coated. Set aside to come to room temperature, at least 20 minutes and up to 45 minutes.
Position a rack in the center of the oven and heat the oven to 350°F.
Heat a 12-inch cast-iron skillet over medium-high heat until very hot, about 2 minutes. Add the oil, swirling the pan to coat the bottom; then add the steaks and cook, undisturbed, until nicely browned on the bottom, about 4 minutes. Flip and cook, undisturbed, until nicely browned on the other side, about 4 minutes. Transfer the skillet to the oven and cook until an instant-read thermometer registers 120° to 125°F for rare, 130° to 135°F for medium rare, or 140° to 145°F for medium, 2 to 7 minutes. Let the steaks rest on a plate, loosely covered with foil, for 5 minutes. Serve the steaks topped with the chimichurri sauce.