In a pan, fry the ginger in oil. Add the garlic, onion and tomatoes. Sauté well. Add the mashed tahure and some water. Let it simmer for a bit. Before you add the vinegar, taste. Add patis or fish sauce if needed. Totso is slighty salty with a hint of sour. You balance these two flavors. A bit of caution: once you add the vinegar, do not stir until after it starts boiling again. The older cooks will tell you mahihilaw iyong suka (the vinegar will not cook) if you do otherwise and no matter how long you simmer it, the vinegary taste will not blend well with the rest of the dish. Taste again if you have achieved that balance between salty and sour that is characteristic of totso. Correct by adding what is lacking. Once the taste seems right to you, add the bangus. Simmer for about five minutes at least. Then done.