Heat oil in a pan put chopped onion, fry until golden brown, add tomatoes n dry red chili and salt,, cook for a mint..
Remove form flame,.. Pour this into a chutney jar. Add some water if u want. Grind this to make a smooth paste..
Now pour this into a bowl.
Then heat oil in a tadka pan add mustered seeds n curry leaves n add into tomato chutney.....