Brown the lamb and the onion together, breaking up the lamb until both are cooked.
Add all of the spices, and stir to coat. Cook for one minute, or until fragrant.
Add the tomato paste, and stir into the mixture.
Add all remaining ingredients, simmer for at least 10 minutes.
Season to taste with salt and pepper.
Serve on brioche buns. Top with yogurt, pickled onion and cilantro.