Pulse the onion, ginger, garlic, coriander, and chillies in a hand blender until roughly chopped.
Mix the chopped aromatics with lamb mince, cumin, garam masala, salt, egg, and breadcrumbs in a bowl.
Shape the mixture into six burgers and chill in the fridge for 20 minutes.
Combine yoghurt, coriander, mint, green chillies, salt, and pepper in a bowl to make the sauce.
Preheat the grill to high and oil a baking sheet.
Cook burgers for 5 minutes per side under the grill or 10 minutes total in a pan.
Heat the buns in the oven during the final 4 minutes of burger cooking.
Assemble burgers with lettuce, tomatoes, onion rings, and a spoonful of herbed yoghurt on split buns.