In a blender, combine the garlic, chipotles in adobo, olive oil, apple cider vinegar, chili powder, cumin, oregano, black pepper, and salt. Blend until you get a smooth sauce. Add a splash of water if needed to make blending easier.
To a gallon-sized ziptop bag, add the steak and cover it with sauce. Seal the Ziploc bag, and marinate in the fridge for 30 minutes to 24 hours.
Remove the steak from the fridge about 30 minutes before cooking to allow it to reach room temperature.
Preheat your cast iron skillet over medium-high heat. Add a tablespoon of light olive oil or avocado oil.
If cooking peppers, add bell peppers and onions, season with salt and pepper and squeeze half a lime. Sauté over medium heat until they are soft and slightly caramelized, about 10 minutes. Remove onto a plate and set aside.
Add more oil if needed, then add your steak. Cook for about 3-5 minutes on each side for medium-rare or until your desired doneness (I aim for 125-135°F).
Once done, remove the steak from the skillet and let it rest for about 10 minutes.
Slice the rested steak against the grain into strips and then diagonally into cubes.