Mix suji, curd and 1/4 tsp salt in a bowl adding a little water to make idli batter. Rest for 10 mins. After 10 mins add eno to the idli batter and mix well. Grease the idli moulds and then Pour the idli batter in the idli moulds. Steam for 10 mins. Let the idli stand cool then take off the idlis and keep aside.
Filling: heat oil in a kadhai. Add cumin seeds and mustard seeds. Let it splutter then add green chillis and ginger garlic paste. Stir then add all the dry masalas and salt to taste. Mix well till raw smell goes off. Then add green peas stir. Cover for 5 mins and cook on low flame. When the green peas are cooked then add mashed boiled potato. Mix well. Remove from flame. Let it cool.
Sandwich: now spread the potato filling on one idli cover with another idli. Brush oil in a pan. Heat. Pour some mustard seeds on it. Let it splutter. Then toast all idli sandwich from both sides till golden. Serve with chutney or sauce.
