Heat the oil in a small saucepan, then add the mustard seeds. Once they have popped, tip in the onion and chillies and stir for a minute.
Then add the turmeric, sugar, cumin and salt and continue to fry for 1 minute. Pour in the yogurt and lemon juice, stirring continuously.
Lastly, fold in the bread carefully so that it doesn't crumble too much.
Cook for 2 more minutes, then serve sprinkled with coriander and chopped tomato.
Tip: Dollop some extra yogurt over the finished dish to cool it.