Using a damp paper towel, gently wipe tops of mushrooms. Slice each mushroom in half and then set aside.
In a heavy pan, heat the oil over medium high heat. Add the pork and cook, stirring occasionally, until brown, about 4 minutes.
Add the vinegar, soy sauce, water, garlic, bay leaves and pepper. Boil, without stirring and then lower heat to medium. Cover and cook, stirring occasionally, for 40 minutes or until pork is tender.
Add the mushrooms and cook until tender, about 5 minutes.
Serve with rice.