Spray slow cooker with cooking spray and place the pork on the bottom. Pour the water and bouillon. Place onions around the roast. Cover and cook on low 7-10 hours. The pork should be tender and easy to shred.
When pork is finished drain the juices and discard onions. Shred the meat.
Combine soy sauce, Worchestershire, garllic, brown sugar and oyster sauce. Pour over the meat and stir.
Let it cook for another 30 minutes so that the flavors are blended.