In a medium bowl whisk together lime juice, orange juice, olive oil, soy sauce (or Worcestershire), minced garlic, chopped cilantro, ground cumin, dried oregano, chili powder, salt, black pepper and lime zest if using. Taste quickly and adjust salt/acid as needed.

Marinate the steak

Place the skirt or flank steak in a large shallow dish or heavy resealable plastic bag. Pour the marinade over the meat, turning to coat thoroughly. Press out excess air (if using a bag) and refrigerate. Marinate at least 1 hour, ideally 4–6 hours; do not exceed 24 hours to avoid overly tenderizing the meat.

Bring to room temperature

About 30 minutes before cooking remove the steak from the refrigerator so it comes closer to room temperature. Reserve marinade for basting (if desired) or discard.

Cook & Assemble

Preheat grill or skillet

Preheat a grill to high heat (500°F/260°C if measured) or set a heavy cast-iron skillet over high heat on the stovetop. Brush the grill grates or skillet lightly with vegetable oil to prevent sticking.

Pat steak dry and season

Remove steak from marinade and pat both sides dry with paper towels — a dry surface sears better. Lightly brush or rub with the tablespoon of vegetable oil and sprinkle a little extra salt and pepper on both sides if desired.

Sear the steak

Place the steak on the hot grill or in the skillet. Cook 3–5 minutes per side for medium-rare to medium depending on thickness: skirt steak around 3–4 minutes per side, thicker flank steak 4–6 minutes per side. Use an instant-read thermometer if desired: 125–130°F (52–54°C) for medium-rare, 135°F (57°C) for medium. Avoid constant flipping; let a good crust form.

Rest and slice

Transfer the cooked steak to a cutting board and let rest 8–10 minutes tented loosely with foil. This redistributes juices. Slice thinly against the grain into 1/4-inch slices for maximum tenderness.

Warm tortillas and serve

Warm tortillas on the hot grill or in a dry skillet for 20–30 seconds per side until pliable and slightly charred in spots. Arrange tortillas, sliced steak, chopped onion, cilantro, lime wedges, salsa/pico de gallo and optional queso fresco or avocado for serving. Assemble tacos: top warm tortilla with sliced asada, sprinkle with onion and cilantro, squeeze lime juice over, and add salsa.