Combine all ingredients in Chimichurri sauce into food processor. Blend until smooth.
Store in an air tight container until after steak is cooked.
Flank Steak Marinade
In a small glass bowl, combine all ingredients for marinade until well blended.
Place steak and marinade in an air tight container. Allow steak to marinade for 1 hour and up to overnight.
Cooking Flank Steak
Start with a very hot skillet, medium high heat. Preferably a cast iron skillet or one of the many types cast iron pans. I use this indoor grill iron skillet that I place on the stove top.
After it heats up, lightly coat the indoor grill with olive oil or a nonstick spray. Immediately place the marinated steak on the grill. It should be hot enough that it immediately begins to sizzle. You'll need that to have a seared flank steak.
Cook flank steak for 3-4 minutes before turning it. Look for the dark brown almost black charred look before turning.
Continue to cook for additional 3-4, depending the thickness your cut of meat.
Remove from the grill and place on a cutting board. Let the meat rest for 10 minutes before slicing to allow the juices to distribute.