To make the marinade, in the bowl of a food processor or blender, add garlic, adobo sauce, ancho chile powder, olive oil, cumin, dried oregano, 1 tablespoon salt, and 1 teaspoon pepper. Blend until smooth (add water if needed to fully blend the marinade).
In a large zipper-top plastic bag or bowl, add steak and marinade, tossing to coat. Let the beef marinate at room temperature for 30 minutes or up to 12 hours in the refrigerator. Bring to room temperature for at least 30 minutes before cooking.
In a large skillet over medium-high heat, heat 2 tablespoons olive oil until shimmering. Add marinated steak to the skillet and cook, stirring occasionally, until the temperature reaches 135 degrees for rare or 145 degrees for medium-rare. Depending on the size of your skillet, you can cook the steak in batches.
Remove to a cutting board and tent with foil for 10 minutes. Chop into small pieces. Season to taste with salt. Serve with your favorite burrito toppings such as rice, beans, guacamole, and salsa.
Adobo sauce: To make your own adobo sauce, whisk together 1 tablespoon tomato paste, 1 tablespoon cider vinegar, 1 teaspoon chipotle powder (or ½ teaspoon EACH smoked paprika and cayenne powder), ½ teaspoon ground cumin, and a pinch EACH of oregano, garlic powder, and salt.
Olive oil: Chipotle uses rice bran oil, but olive oil is more widely available (and probably already in your pantry).
Oregano: Chipotle uses Mexican oregano, but you can use Italian oregano if that’s all that you have. They have different flavors (Mexican oregano tastes more like marjoram) but both taste great in this recipe.
Steak: According to Chipotle's customer service, the "beef" in their steak could be any number of cuts including part of the loin, ball tip, round steak, flat iron steak, top butt, clod, or knuckle.
Yield: This recipe makes 20 generous 1/2-cup servings.
Storage: Store leftovers covered for up to 4 days.
Make ahead: The steak can be marinated the day before you need it. Store it in an airtight container in the refrigerator and bring to room temperature for 30 minutes before cooking.
To substitute dried ancho chiles:
Remove stems and seeds from dried chiles (wearing gloves is recommended).
In a dry skillet over medium-low heat, toast the chiles until fragrant but not smoking, about 5 minutes.
Transfer to a medium bowl and add 4 cups (1 quart) water and 2 Tablespoons adobo sauce. Microwave on HIGH for 6 minutes. Drain well, then add the chiles to the food processor in step 1.