Make the marinade. Juice the lime directly into the blender. Add the olive oil, soy sauce, garlic cloves, brown sugar, salt, and pepper. Blend on high for approximately 1 minute until the mixture is fully emulsified and has a consistent, creamy texture similar to a thin peanut butter. The color should be a pale green-brown.
Marinate the steak. Place the skirt steak in a large resealable zip-lock bag. Pour the marinade in, press out as much air as possible, and seal the bag. Move the bag around to make sure the steak is completely coated on all sides. Refrigerate for 6 to 12 hours. Overnight is ideal.
Prep for grilling. Pull the steak out of the refrigerator 20 to 30 minutes before cooking to take the chill off. Preheat your grill on high for at least 15 minutes. Remove the steak from the marinade, let the excess drip off, and pat the surface dry with paper towels.
Grill the steak. Place the steak on the hot grill and cook 3 to 4 minutes per side for medium, depending on thickness. Do not move it around — let it sear undisturbed on each side. Pull at 130 to 135°F for medium-rare or 140°F for medium.
Rest and slice. Transfer the steak to a cutting board and let it rest for 5 minutes. Slice thin against the grain at a slight angle.
Serve. Use immediately for tacos, burrito bowls, or serve sliced alongside rice and beans.