Step 1

Cut ½ medium head of cabbage in half lengthwise and remove core; discard. Slice cabbage crosswise into very thin strips (as thin as you can). Transfer to a large bowl and sprinkle with ½ tsp. Diamond Crystal or ¼ tsp. (heaping) Morton kosher salt. Massage gently with your hands to work in salt and soften cabbage a bit. Set aside.

Step 2

Toast 5 unpeeled garlic cloves in a dry small skillet over medium-high heat, until skins are deeply charred on both sides, 5–7 minutes. Let cool a few minutes and peel garlic. Place in blender along with 2–3 canned chipotle chiles in adobo (add 3 if spicy is your thing) and 1 Tbsp. adobo sauce, ⅓ cup (packed) dark brown sugar, 2 Tbsp. distilled white vinegar, 1 tsp. Diamond Crystal or ½ tsp. (heaping) Morton kosher salt, ½ tsp. freshly ground black pepper, and ½ cup water. Blend until smooth. Transfer salsa to a small bowl.

Step 3

Prepare a grill for medium heat. Clean and oil grate. Season 1½ lb. boneless beef short ribs, preferably 1" thick, with remaining 2 tsp. Diamond Crystal or 1¼ tsp. Morton kosher salt; drizzle evenly with vegetable oil. Grill, rotating every minute or so, until exterior is deeply browned and crisp and an instant-read thermometer inserted into the thickest part registers 120°, 7–12 minutes, depending on the thickness of your ribs. Brush ribs with salsa and continue to grill, turning every minute or less, until shiny, glazed, and thermometer registers 130°, about 3 minutes. Transfer to a cutting board and let rest 20 minutes.

Step 4

If you don’t have a grill: Heat 2 Tbsp. vegetable oil in a large cast-iron skillet over medium-high. Season 1½ lb. boneless beef short ribs, preferably 1" thick, with remaining 2 tsp. Diamond Crystal or 1¼ tsp. Morton kosher salt (no need to rub with oil) and cook, turning every minute or so, until exterior is deeply browned and crisp and an instant-read thermometer inserted into the thickest part registers 125°, 5–10 minutes, depending on the thickness of your ribs. Brush with salsa and continue to cook until glaze has darkened in color, about 15 seconds per side. Repeat process with another layer of salsa. Transfer to a cutting board and let rest 20 minutes.

Step 5

While the meat is resting, prepare the garnishes. Cut 1 large red onion in half through the root end and remove skin. Slice halves through root end into ½"-thick wedges (this will keep layers together while grilling). Grill onion wedges until charred (or cook in the same skillet—no need to clean), about 2 minutes per side. Trim root so layers easily separate and arrange on a platter. Cut 1 lime in half and squeeze juice into cabbage. Add 1 cup (lightly packed) cilantro leaves with tender stems to slaw and toss to combine. Slice 1 avocado and arrange on a small plate. Char 10–14 tortillas on grill or toast in a dry skillet, about 15 seconds per side. Wrap in a kitchen towel to keep warm .

Step 6

If short ribs are very thick, slice horizontally through the middle of the sides into 2 thinner pieces, then slice against the grain ¼" thick. Rotate slices 90° and chop crosswise into ¼" pieces. Arrange on platter next to onion and serve with cabbage slaw, avocado, tortillas, and remaining salsa for making tacos.

Step 7

Do ahead: Cabbage can be salted 1 day ahead; cover and chill. Salsa can be made 1 week ahead; cover and chill.