In a bowl combine the ingredients for the marinade and mix well.
Pour the marinade into a ziplock bag and add the steak ensuring the meat is fully covered. Place in the refrigerator for at least 6 hours and preferably overnight.
Take the steak with marinade out of the fridge and allow it to come to room temperature. (approximately 2 hours).
Place a large frying pan next to your cast Iron skillet and warm the tortillas over a medium heat one or two at a time. If you need to heat the tortillas faster, you can wrap them in foil and place them in the oven at 200 degrees. Be sure not to completely seal the foil as the tortillas will release moisture and become soggy.
Place a cast iron skillet on a medium-high fire and add 1 tbsp of oil. Place the steak in the skillet and sear for approximately 3 minutes per side. Remove the steak from the pan and let it rest in a cutting board tented with aluminum foil.
While the steak rests, add a tablespoon of oil to the pan. When the oil is at temperature, add the onions and peppers and cook for 4 to 5 minutes or until onions are translucent. Add salt and pepper to taste.
Slice the steak against the grain into thin slices. Add the steak to the pan and mix with the onions and peppers. Turn the fire back on and cook for about a minute. Add cilantro and serve with warm tortillas, Mexican salsas, and guacamole.
Enjoy!