In a medium bowl, combine the kosher salt, chili powder, smoked paprika, sweet paprika, ground cumin, dried oregano, garlic powder, onion powder, ground coriander, black pepper, crushed red pepper flakes, cayenne pepper, and brown sugar (if using). Stir well with a fork or small whisk, breaking up any clumps. If your oregano is in big pieces, crush it between your fingers as you add it for better texture and aroma.

Taste a tiny pinch of the dry seasoning mix (on a bit of plain rice or a cracker if you prefer). Adjust by adding more salt, black pepper, or chili heat (red pepper flakes or cayenne) to suit your taste and to account for differences between brands of chili powder.

Transfer the carne asada seasoning to an airtight jar or spice container, label it, and store in a cool, dark place such as a pantry or cupboard. For best flavor, use within 3–6 months, though it will remain safe to eat for up to a year with gradually reduced potency.

Pat your flank, skirt, or flap steak dry with paper towels. Sprinkle 1–2 tablespoons of seasoning per pound of meat, coating both sides evenly. Gently press the rub into the surface of the steak. Let it rest at room temperature for 20–30 minutes before grilling or searing so the seasoning adheres and the meat takes off the chill.

In a bowl or large measuring cup, whisk together 3 tablespoons of the carne asada seasoning, fresh lime juice, orange juice, neutral oil, minced fresh garlic, and chopped cilantro (if using). Taste a drop of the marinade and, if it’s too tart, add a teaspoon of oil or a tiny pinch of brown sugar to balance.

Place 2–3 pounds of flank steak, skirt steak, or flap meat in a large zip-top bag or shallow dish. Pour the marinade over the meat, turning to coat both sides evenly. Press out excess air, seal, and refrigerate for at least 1–2 hours and up to 8 hours. Avoid marinating longer than 8–10 hours, as the citrus acid can start to break down the texture too much.

Heat a grill to medium-high (about 450–500°F) or preheat a cast iron pan until very hot. Shake off excess marinade from the steak and cook for 3–6 minutes per side, depending on thickness and desired doneness. Aim for medium-rare to medium for the juiciest results. Transfer the steak to a cutting board and let it rest for 5–10 minutes before slicing.

Slice the rested steak thinly against the grain. Serve in warm tortillas for tacos, over rice bowls, or in burritos, quesadillas, and nachos. Finish with a squeeze of lime and toppings like chopped onion and cilantro if desired.