Combine the marinade ingredients into a small bowl and mix together. Pour mixture into a gallon size zip-top bag.
Add the sliced meat to the bag and close. Use your hands to move the meat around in the mixture. Marinate for at least 2 hours (more is better) in the refrigerator until ready to cook.
Melt butter (or fat of choice) in a large cast iron skillet over medium-high heat. When the pan is hot and the butter melted, transfer the sliced meat from the marinade into the skillet using tongs. Discard the remaining marinade.
Cook the meat for about 6 minutes, or until cooked through. Flip the meat periodically to prevent burning.
Transfer the meat to a large plate and set aside. Turn the heat down to medium.
Add the bell peppers and onion to the skillet and toss to coat with the liquid that remained.
Sprinkle the remaining seasoning (except the cilantro) over the vegetables and toss to combine. Cook for 5 minutes or until the vegetables are cooked to your liking. Stir often.
Add the meat back to the skillet to reheat and mix with the vegetables. Garnish with cilantro (optional) and serve.
