Trim the Outside Skirt Steak (Optional)

1. If your steak is already well trimmed, skip this step.
2. Pat the outside skirt steak dry with paper towels, then trim off any thick or loose pieces of fat. Don’t overdo it. Just remove anything that looks excessive.
3. Flip the steak to the other side and run your fingers along the surface; you may notice a thin, silvery membrane. If you find it, grab an edge with a paper towel and peel it away. It usually comes off in big pieces. If you can’t find it, don’t worry about it and move on. Remember, skirt steak is a thin cut, so it’s better to undertrim than overtrim.

Portion the Steak into Smaller Pieces

1. Cut the steak with the grain into 5- to 6-inch (13- to 15-cm) pieces so they fit comfortably in the pan. As you portion it, try to keep each piece fairly even in thickness from end to end. This helps the pieces cook more evenly.

Dry-brine the Steaks

1. Pat the steak pieces dry with paper towels and season both sides lightly with salt. Place them on a wire rack set over a baking sheet and refrigerate uncovered for at least 1 hour, preferably 2 to 4 hours.
2. While the steak dry-brines, prepare the salsa roja.

Make the Salsa Roja

1. Wash all the ingredients first. Cut the tomatoes in half, quarter the onion, and peel the garlic cloves. Choose one of the methods below to char the vegetables. Charring creates quite a bit of smoke, so turn on your exhaust fan or open a window before you start.
2. On the stovetop: Heat a 12-inch (30 cm) skillet over medium-high heat for about 2 minutes. Add the tomatoes, onion, garlic, and peppers and cook, turning occasionally, until well charred on all sides.
3. Under the broiler: Arrange the tomatoes, onion, garlic, and peppers on a baking sheet. Place it close under the broiler and broil on high, turning as needed, until well charred.
4. Transfer the charred vegetables to a food processor. Add the cilantro, lime juice, olive oil, and salt, then blend to your preferred consistency. Taste and adjust the salt as needed. Transfer to a container, cover, and refrigerate until ready to use. (See Notes for make-ahead, storage, and consistency tips).

Preheat the Pan

1. Take the steak pieces and salsa roja out of the refrigerator about 15 minutes before you start cooking and let them sit at room temperature.
2. Turn on your exhaust fan or open a window, since searing over high heat gets smoky. Heat a heavy skillet over medium-high heat for 3 minutes. Add 2 tablespoons of oil and heat for 1 minute more.
3. While the skillet heats, pat the steak pieces dry again with paper towels to remove any surface moisture.

Sear the Steak Pieces

1. Carefully place as many steak pieces as will fit flat in the skillet without touching or overlapping. Work in batches rather than overcrowding the pan. Sear, flipping every 30 seconds.
2. After about 2 minutes, start checking the internal temperature of each piece. Because the pieces vary in thickness, check them individually and remove each one as soon as it reaches the pull temperature for your preferred doneness: 110°F (43°C) for rare, 120°F (49°C) for medium-rare, 130°F (54°C) for medium, 140°F (60°C) for medium-well, 150°F (66°C) for well-done. See the complete steak temperature chart above the recipe card.
3. Transfer each steak piece to a cutting board as it reaches the correct temperature and let it rest for 5 minutes.

Assemble the Tacos

1. Once the steak pieces have rested, slice them thinly into strips, then dice the strips into small, bite-sized pieces.
2. Warm the tortillas until soft and pliable. You can warm them in a dry skillet, in the oven, in the microwave, or directly over a gas burner using tongs.
3. Divide the chopped steak among the tortillas, then top with salsa roja, finely chopped onion, chopped cilantro, and a squeeze of lime juice. Serve immediately.