Keep on direct flame or use a wire mash over flame .
Grill till they are charred from all sides and tomatoes become soft.Chilis need less time as compared to tomatoes so remove them as soon as they are charred.
Let them come to room temperature then chop them roughly and if you want to remove the skin then remove before chopping.
Put tomatoes,chili and chopped coriander in a chopper or in a mixer jar and crush coarsely.
Now add salt and mustard oil and mix well.
Transfer in a glass jar or container and serve as a side dish or accompaniment.
Stay well for 3-4 days in the refrigerator.
Notes
Note-Can also add few drops of lemon juice and a pinch of sugar .