Mix the pork, cornstarch, and soy sauce in a small bowl. Let it marinade 10-30 minutes while you prepare the other ingredients.
Heat the oil over medium heat. Saute the ginger and garlic for 1-2 minutes. If the oil is too hot, the garlic will sizzle and pop oily garlic bits onto your skin, making for those exciting little pin prick garlic-oil burns. If that's the case, put the meat in before the 1-2 minutes are up. Stir fry pork 2 minutes or so, until lightly browned and almost cooked.
Add the black bean sauce mixture. Stir for a minute or so, scraping up any pork stuck to the pan. Add the veggies, cook for about 3 minutes.
Add the cornstarch and sherry sauce mixture. Cook for another 1-2 minutes until the sauce is thickened and the cornstarch is clear. Add extra water to make the sauce the consistency you like.
Serve hot over fresh rice.