Mix all the ingredients together in the slow cooker, apart from the spinach, if using.
Set off on low for 6-8 hours, or until the lamb is soft and tender. If you are adding spinach, lift the lid and stir in and leave to cook for a further 20 minutes.
Serve with rice and naan bread.
Notes
Curry Paste - you can use your favourite curry paste for this, madras is a popular one with lamb, but if it’s too hot, use a milder one such as korma. Increase or reduce the amount of curry paste you add according to your own taste.