Combine the leftover rice, besan, rice flour, chopped onion, green chili, coriander leaves, and salt in a bowl. Mix well to form a thick batter. Add water if needed. Heat a non-stick pan and drizzle oil. Take a ladleful of the batter and spread it evenly on the pan. Cook until both sides turn golden brown. Serve with mint chutney or tomato ketchup.