
In a large, resealable Ziplock bag, put in all the marinade ingredients, adding the beef last. Massage the marinade into the beef for 2 minutes. Make sure the bag is sealed well and refrigerate overnight or for 12 hours.
30 minutes before cooking, remove the beef from the marinade and place in a bowl on the counter. Pat it dry with paper towels and discard the marinade. Drizzle 1 Tablespoon of olive oil over the meat, on both sides, and then cook on the barbecue or in a skillet on high heat. Cook to your own preference.
When done cooking, place the beef on a plate and cover loosely with foil. If you cooked the beef in a skillet, use that one for the next step. But if you barbecued the beef, grab a skillet and place it on the stove.
Heart 1/2 Tablespoon of olive oil in the skillet until it's hot and then add the onions. Saute and season with salt and pepper. Cook onions until soft and they begin to caramelize. Remove the onions to a serving plate.
Heat the last 1/2 Tablespoon of olive oil in the skillet and saute the peppers and season with salt and pepper. Cook until lightly charred and remove to a serving plate.
Slice the meat thinly, against the grain. Serve the meat on warm tortillas with onions, peppers, and your favorite fixings.