Place a large skillet over medium-high heat with the oil. Working in batches, sear off the meat, browning well on all sides, about 15 minutes total.
Transfer the meat to the crock of a slow cooker and add the fish sauce and enough coconut water to cover the meat by about two-thirds (NOTE: This dish can be prepared up to this point and then stored in the refrigerator overnight to be cooked the next day).
Turn on the slow cooker and simmer the meat until fork tender, about 6 hours on high heat or 8 hours on low heat. Serve warm with a few spoonfuls of the braising liquid and a hearty garnish of cilantro and scallion.
This dish is incredibly satisfying but very rich. Temper its heartiness and make it into a complete meal with a side serving of steamed white rice.
Don't cut corners on browning the meat off - if anything, let it sear a bit longer than you think you should. It's a critical cornerstone to keeping the flavor of this dish from washing out in the slow cooker.
If you don't own a slow cooker, you can still prepare this dish on the stovetop. Simply sear off the meat in a heavy-bottomed Dutch oven, add the liquids to the pot and bring them to a boil. Reduce the heat to medium-low and simmer until the meat is fork tender, about 2 hours.