Preheat oven to 350°F.
Heat grapeseed oil in Dutch oven over medium-high heat on stovetop. Working in batches, brown short ribs on all sides. Remove and set aside.
Add diced onion to the same pot. Cook 2-4 minutes until fragrant. Add crushed garlic and cook another 1-2 minutes.
Add beef broth, diced tomatoes, chipotles in adobo, apple cider vinegar, salt, Italian seasoning, and brown sugar. Bring to boil and return ribs to pot.
Cover and bake 2½ hours or until meat shreds easily and falls off the bone.
While ribs cook, make salsa by combining tomatillos, serrano peppers, avocados, garlic, and cilantro in a food processor. Pulse until smooth. Add lime juice and season with salt to taste.
Remove ribs from pot and cover with foil. Return Dutch oven to stovetop and skim excess fat. Reduce braising liquid by at least half over medium-high heat.
Shred short ribs and toss with reduced sauce.
Serve on warm tortillas topped with tomatillo-avocado salsa, pickled red onions, cotija cheese, and lime wedges.
