Slice the tomatoes, smear turmeric and salt on them and soak them in 1 cup vinegar. Leave for about 2 hours.
Blend together the garlic, ginger, red chilies and 3/4 of the mustard, with a little vinegar.
Heat the oil and add the remaining mustard. When the mustard crackles, add the fenugreek seeds.
Fry for 2 minutes and then add the blended mixture. Fry well for over 20 minutes.
Add the tomatoes and the remaining vinegar. Stir continuously as the mixture comes to a boil.
When the pickle is almost done, the oil begins to float at the top.
Take it off the heat and let it cool. Store in a clean bottle. Will last for a year.