Trim the edges of the bread slices. Soak the slices in sufficient water for two to three minutes. Take semolina, rice flour, salt and add sufficient water to make a thin batter. Squeeze out excess water from the soaked bread and lightly crumble with hand.
Add it to the batter along with whisked yogurt. Put the mixture in a mixer and blend. Transfer to a clean bowl and adjust the consistency.
Heat two tablespoons of oil in a pan. Add mustard seeds, dhuli urad dal, curry leaves, chopped ginger, green chillies, onion and sauté till onions are lightly browned. Set aside to cool. Heat a dosa tawa.
Put some oil on it and wipe with a clean wet cloth. Add the tempering to the batter and mix well. Pour a ladleful of the batter onto the hot tawa and spread.
Pour a little oil on top and sides and cook for two to three minutes. Turn and cook the other side similarly. Prepare the other dosas similarly. Serve hot with chutney.