In a bowl, combine pork and soy sauce and set aside for about 30 minutes.

Heat the oil in a wok and saute the garlic till light brown. Add the onion and cook till transparent and then add the sliced tomatoes. Saute until vegetables are soft, then add the pork/soy sauce mixture. Saute for a while until the flavor of the sauteed ingredients absorb by the pork.

Add a cup of water. Stir, then add the whole peppercorns and ground black pepper and salt, then cover the wok and let the pork simmer on low heat until the pork is tender. Just stir and check often so the sauce won't dry out. Add a little bit of water at time while simmering, and when the pork is tender, add the vinegar.

Cook, covered until the aroma of raw vinegar vanished, then that's the time you can stir the pork mixture again. The amount of vinegar varies, it depends on how acidic your vinegar is.

Check the seasonings. Add more soy sauce if needed. Add more or less water, it depends on how much sauce you want, or you can cook it till the sauce dries out a little, either way it's good.