Place the steak in a large shallow dish and pat it dry with a paper towel.
Add the parsley, garlic, lemon juice, oregano, red pepper flakes, salt and pepper to a food processor and pulse for about 10-15 seconds on low speed.
Then add the ½ cup of olive oil and pulse again until thoroughly combined.
Pour 2-3 tablespoons of chimichurri over the raw steak and spread evenly around he top of the steak and allow to marinate at room temperature for 15 minutes.
Remove the steak from the marinade and pat it dry with a paper towel.
Heat one tablespoon of olive oil in a cast iron skillet over medium-high heat.
Carefully add the steak and sear on the first side for 2 minutes.
Flip the steak and sear on the other side for an additional 2 minutes for medium rare . (longer if steak is thicker than 1 inch)
Remove the steak and place on a plate and cover with aluminum foil.
Allow the steak to rest for 5 minutes before slicing.
Serve hot topped with chimichurri sauce.