First make the quick pickles: Add all of the vegetables to a jar with a tight fitting lid. To a sauce pot, add the water, vinegar, smashed garlic, cilantro, red pepper flakes, salt and sugar. Bring to a simmer to dissolve sugar and salt.
Pour vinegar mixture over the vegetables and let sit on the counter until it comes to room temp. Cover and place in the refrigerator.
For the beef: Preheat oven to 325 degrees.
Heat a large pot over medium high heat. Add oil. Season the beef with salt and pepper and cook on each side, searing until a brown crust forms, about 5 to 7 minutes per side. Remove and set aside.
To the same pan add the onion, garlic and ginger and saute for about 5 minutes. Stir in beef broth, soy sauce, gochujang and honey. Place meat back in the pan and bring to a boil. Place pot in the oven, cover, and cook for 2 1/2 hours.
When beef is done, remove from oven and allow to cool slightly. Use two forks to shred the meat in the braising liquid.
To assemble tacos, place some meat in the center of each cabbage leaf and top with pickled vegetables. Garnish with scallions.