In bowl, mix 1 cup water and oyster sauce. Heat wok or large skillet over high. Add 1 tbsp. oil, then add pork; cook until golden, 2 minutes. Transfer pork to a plate. Add 2 tbsp. oil to wok, then add broccoli and mushrooms. Cook, stirring, 2 minutes. Stir in garlic, ginger and oyster sauce mixture and cook 3 minutes. Return pork and juices to wok. Stir 1 to 2 minutes to heat pork through; season.