1. Put lentils in a bowl, add water and leave to soak for 2 hours.
2. Put lentils, their soaking water, 2 onions, lamb, garam masala and red chillies in a large heavy-based pan bring to the boil.
3. Cook, uncovered, over a medium heat, stirring constantly, until all the liquid has evaporated and mixture is very dry.
4. Remove from heat and leave to cool.
5. Put mixture in a blender or food processor fitted with a metal blade and process to a smooth paste.
6. Add egg and yogurt and blend again.
7. Chill for 2-3 hours, then form into 16 balls.
8. Mix together remaining onion, mint and green chillies.
9. Make an indentation in each lamb ball and stuff with a little minty mixture, then cover up with meat.
10. Flatten balls into 5 cm (2 in) patties.
11. Heat oil in a frying pan and fry patties a few at a time for 4-6 minutes, turning over after half the time, until well browned.
Serve, garnished with fresh mint leaves.

Serves 4.