Pat the steak dry with a paper towel and place it in a large, shallow dish.
Add the parsley, garlic, lemon juice, oregano, and red pepper flakes to the bowl of a food processor and pulse until finely chopped-- about 10-15 seconds.
With the processor on low, slowly add in the ½ cup of olive oil and pulse until it is well combined.
Season with salt and pepper to taste.
Add ¼ of the chimichurri over the raw steak, reserving the rest to top the steak after it has been cooked.
Allow the steak to marinate for 15 minutes at room temperature.
Remove the steak from the marinade and pat it dry with a paper towel. Season it with salt and pepper.
Heat a cast iron or heavy-bottomed skillet (non-stick is not recommended here) over mediumhigh heat. Add the olive oil and allow it to heat until the oil starts to ripple.
Carefully add the steak and sear on the first side-- see the notes section for cooking times based on your steak’s thickness. Then, flip the steak and sear it on the second side.
Remove the steak and place it on a cutting board and cover it with foil. Allow it to rest for 5 minutes before slicing. Serve hot, with chimichurri on top.