Combine all the marinade ingredients and pour half into a non metallic dish. Add the steaks and set aside to marinate for an hour. Reserve the remaining marinade which is the chimichurri sauce.
If using a barbecue get it very hot, or preheat a griddle pan. Warm the tortillas.
Remove the steaks from the marinade and season with salt and pepper. Cook on a hot barbecue or griddle pan for about 2 minutes on each side for medium rare, or until done to your liking. Remove to a warmed plate and rest for five minutes before cutting.
Slice the steaks across the grain and serve with the warmed tortillas, sour cream, salad and salsa. Serve the chimichurri sauce alongside to spoon overe the steak and salad.