Boil the tomatoes,drain and peel its skin off.you can also smoke the tomatoes instead,which give a nice smoky taste.Grind this with coconut,green chilly and salt,to a smooth paste.
Mix lemon juice.Heat oil in a pan add the mustard seeds when it starts splattering add the ground paste mix it nicely.Switch off the fire.Cool it aside.Serve as a dip for Toasted Bread,Chapattis,or any other dish of your choice,it tastes terrific..