Build your marinade first. In a large bowl, whisk together the lime juice, orange juice, avocado oil, minced garlic, soy sauce, cumin, smoked paprika, ancho chili powder, oregano, black pepper, salt, and red pepper flakes if using. Stir in the chopped cilantro and sliced jalapeno. The marinade should smell bold and bright. Taste it - it should have a sharp citrus bite with a warm, savory backbone. Adjust salt or citrus to your preference.

Prepare the skirt steak. If your skirt steak is longer than 10 to 12 inches, cut it into manageable pieces so it fits flat on the grill. Lightly score the surface of the meat with shallow diagonal cuts about half an inch apart, which helps the marinade penetrate deeper into the muscle fibers. Place the steak in a large zip-top bag or baking dish and pour the marinade over it, making sure every surface is well coated.

Marinate the steak. Seal the bag or cover the dish and refrigerate for a minimum of 2 hours, but ideally 6 to 12 hours overnight. Do not marinate longer than 24 hours or the citrus acids will start to break the texture down too aggressively and you will end up with a mushy exterior. About 30 minutes before you are ready to grill, pull the steak out of the refrigerator and let it come toward room temperature on the counter. Cold steak on a hot grill leads to uneven cooking.

Fire up the grill. For authentic carne asada, you want a two-zone charcoal setup with a serious hot side. Fill a chimney starter to the brim with lump charcoal or briquettes and let them ash over until they are glowing orange, about 15 to 20 minutes. Dump all the coals on one side of the grill and position your grates. You are targeting a surface temperature of 500 to 600 degrees Fahrenheit on the hot side. Hold your hand about 6 inches above the grate - you should only be able to keep it there for about 1 second. That is the kind of fire carne asada demands.

Prepare the grates. Once your grill is ripping hot, scrub the grates clean with a wire grill brush. Then, using long tongs, grab a folded paper towel soaked in avocado oil and wipe the grates down quickly. This prevents sticking and helps you get those picture-perfect grill marks. The grates need to be as hot as possible before the steak goes on.

Grill the steak. Remove the skirt steak from the marinade and shake off the excess - you do not want dripping marinade causing flare-ups, though some char from dripping is part of the magic. Lay the steak flat on the hottest part of the grill and do not move it for 3 to 4 minutes. You should hear a loud, aggressive sizzle the moment it hits the grates. Resist the urge to poke or move it. You are building a crust. After 3 to 4 minutes, flip the steak using long tongs and grill the second side for another 3 to 4 minutes.

Check the internal temp. After flipping, start checking the internal temperature with your instant read thermometer. For medium-rare, you are pulling this steak at 125 to 130 degrees Fahrenheit, knowing it will carry over cook during the rest. For medium, pull at 135 degrees Fahrenheit. Skirt steak is best served no higher than medium - anything beyond that and you are losing the tenderness and juiciness that makes carne asada worth making.

Rest the meat. This step is non-negotiable. Transfer the grilled skirt steak to a clean cutting board with a juice groove and tent it loosely with foil. Let it rest the meat for at least 5 minutes. During this time, the internal temp will rise another 5 degrees and the muscle fibers will relax, redistributing all those juices back through the steak. If you cut into it right off the grill, all those precious juices end up on your cutting board instead of in your mouth.

Slice and serve. Here is where most people go wrong with skirt steak: you must slice against the grain. Skirt steak has very long, visible muscle fibers running lengthwise. If you slice with the grain, each bite will be tough and chewy. Look at the direction of the fibers, turn the steak 90 degrees, and slice on a slight diagonal into thin strips about a quarter inch thick. Finish with a pinch of flaky sea salt over the sliced meat and a squeeze of fresh lime juice. Serve immediately while the meat is still steaming hot.