Melt the butter or ghee in a large saucepan over medium high heat. Add the onion. Cook stirring, for 5-7 minutes or until onion begins to brown. Add ginger, garlic, chilli, if using, cumin, coriander and tumeric. Cook , stirring , for 1 minute or until aromatic. Add lamb and cook , stirring with a wooden spoon to break up any lumps, for 5 minutes or until browned and cooked through.
Add the rice and stir to combine. Pour over the stock. Bring to the boil. Reduce heat to low. Cook, covered, for 12 minutes or until rice is tender and liquid is absorbed. Sprinkle with peas. Set aside. covered for 5 minutes.Uncover and use a fork to separate the grains.
To make the Raita, cut cucumber into small pieces. Transfer to a bowl. Stir in the yoghurt and mint . Season.
Transfer the rice mixture to a large serving bowl. Top with cucumber . Serve with raita and cashews.