To prepare the flank steak for the marinade, salt, and pepper both sides of the meat.
In a blender or food processor, place the cilantro, parsley, garlic, oregano, cumin, chili powder, cayenne, salt, and ground pepper. Give the mixture a few pulses to break down the cilantro and parsley. Add 1 cup of the olive oil a little bit at a time through the top opening or add in batches until a nice paste has formed. To the marinade add the chopped onion and the lemon peel. Mix to combine.
In a jumbo size resealable bag, or a shallow non-reactive casserole dish, add half of the marinade mixture. Place the steak on top of the marinade and cover with the rest of the marinade mixture spreading it out to cover. Finish with an additional ½ cup olive oil. Cover and place in the refrigerator at least 8 hours but preferably overnight.
To make the chimichurri, combine the garlic, shallot, chili, salt and the red wine vinegar in a glass bowl and let sit for 20-30 minutes. This will allow the chilies, shallot and garlic to achieve a slight pickling which mellows them nicely. Add the cilantro, parsley, and oregano and mix in well. Finish with adding the olive oil and stirring vigorously to allow all the flavors to combine.