Finely chop the fresh parsley, cilantro (if using), and oregano. Mince the garlic cloves. You can use a food processor for a finer texture, but hand-chopping creates a more rustic sauce.

In a medium bowl, combine the chopped herbs, minced garlic, red wine vinegar, red pepper flakes, salt, and black pepper. Whisk to combine.

Gradually pour in the extra virgin olive oil while whisking continuously until well combined. Taste and adjust seasoning as needed. For best flavor, let the chimichurri sit at room temperature for at least 15-20 minutes to allow the flavors to meld.

Pat the flank or skirt steak dry thoroughly with paper towels. This is crucial for a good sear. Season both sides generously with salt and freshly ground black pepper.

Heat a heavy-bottomed skillet or cast iron pan over high heat for 3-5 minutes until it's smoking hot. Add 1 tablespoon of olive oil to the pan.

Carefully place the seasoned steak into the hot skillet. Sear for 3-5 minutes per side for medium-rare (internal temperature 130-135°F), or 5-7 minutes per side for medium (internal temperature 135-140°F). Cooking time will vary depending on steak thickness and desired doneness. Use a meat thermometer for accuracy.

Once cooked to your liking, remove the steak from the pan and transfer it to a cutting board. Tent it loosely with foil and let it rest for at least 5-10 minutes. This allows the juices to redistribute, resulting in a more tender and flavorful steak.

Slice the steak against the grain into thin strips. Arrange the slices on a platter and spoon a generous amount of fresh chimichurri over the top. Serve immediately with any remaining chimichurri on the side.