Dry roast the tomatoes and chilis in a skillet until nicely roasted on all sides. Stir frequently until browned on all sides.
Let the tomatoes and chilies cool. Peel the tomatoes; chop both the tomatoes and chilies into small pieces. Reserve all the tomato juice.
Heat oil in a pan, add the mustard and fenugreek seeds. Once the seeds start to splutter, add the grated ginger and sliced garlic.
Cook till the garlic is lightly browned all over.
Add the chopped tomatoes, chilis, reserved tomato juice, ground cumin, ground coriander, turmeric and salt.
Cook on medium flame until all the water is evaporated and the chutney gets a nice thick consistency.