For the burgers: Using a hand held blender, roughly chop the onion, ginger, garlic, cilantro, and green chiles by pulsing, or chop them all by hand. Put the mixture into a bowl with the ground lamb, and add the cumin, garam masala, salt, egg, and bread crumbs, and mix well to combine.
Divide the mixture into 6 even portions and shape into burgers, and chill in the refrigerator for 20 minutes, or until you are ready to cook them. Take them out of the refrigerator 30 minutes before you start cooking.
Meanwhile, for the herbed yogurt: Mix together the yogurt, cilantro, mint, and green chiles in a bowl and season with salt, and freshly ground black pepper, to taste.
Preheat the oven to 300 degrees F. Preheat the grill to high.
Place the burgers on a well-oiled baking sheet and cook for about 4 to 5 minutes on each side. They can also be cooked in an oiled nonstick pan for 8 to 10 minutes, turning halfway through the cooking time.
While the burgers are cooking, heat the buns in the oven for the last 3 to 4 minutes of the cooking time.
To serve: Split the buns in half. Place the lettuce onto one half of each bun and top with a burger. Top with the tomatoes and onion rings and a spoonful of the herbed yoghurt. Finish with the other half of each bun.
NotesThis may not sound like an overtly Indian dish and in a way it isn't, but people in India have always eaten kebabs, either as they are or wrapped in flatbread.