Mix all the ingredients except fruit salt in a bowl and keep aside for 10-15 minutes.
Boil some water in an idli steamer.grease the idli moulds.
Once the steamer is ready,add fruit salt to the batter. Mix well and pour into the moulds immediately.
Steam the idlis for 10 minutes or till done. When cool, unmould the idlis.
Heat oil in a kadai, add mustard seeds and let it splutter. Add onions and saute till brown.
Add the carrots and capsicum and stir fry. Add salt and tomato ketchup along with the idlis and toss lightly so that the idlis are coated with the masala.