Add the pork shoulder roast to the slow cooker. Combine dry ingredients of ground ginger, white pepper, cinnamon and nutmeg and rub over shoulder roast.
In a small bowl, combine wet ingredients of soy sauce, sesame oil, shaoxing wine, and fish sauce. Pour over pork and rinse bowl with water and dump over pork again to get any remaining sauce.
Add quartered onion, garlic cloves, limes and bundle of cilantro. Cook on low for 8-10 hours or high for 5-7 until tender.
Shred on a baking sheet and broil for 2-5 minutes until edges are crispy. In a medium saucepan over medium heat, add remaining juices from the slow cooker and whisk in ½ cup brown sugar. Create a slurry in a small cup by mixing 1 tsp corn starch with 1 tsp water. Whisk into sauce to and stir until thickened. Spoon sauce over crispy pork.