To make the marinade, place all ingredients (but steak of course) in a blender and blend until garlic and cilantro is finely minced.
Place the steak in a non-reactive flat bowl or baking dish or freezer-sized ziplock bag. Add blended mixture and turn steak to coat thoroughly.
Cover dish or close bag and refrigerate overnight or up to 36 hours, turning occasionally.
About an hour before grilling, remove steak from refrigerator and bring to room temperature. Prepare a medium-hot fire in a grill or preheat broiler to high.
Cook steak to desired degree of doneness, 3-4 minutes per side for rare. Remove from the heat to a platter and allow it to rest for 10 minutes.
Slice thinly across grain on the diagonal.
About an hour before you plan to serve the steak, place all sauce ingredients but the oil in the bowl of a blender; pulse a few times to chop, drizzling in olive oil as you go. You should be able to spoon the finished mixture, but it shouldn't be runny. Taste and adjust seasoning.
Note: This marinade will help to tenderize the steak as well as provide the unique flavor that makes this steak different.