Heat the oil in the bottom of a large saucepan or your slow cooker if it goes on the stove.
Add the onion and cook until transparent.
Add the garlic, herbs and spices and cook, stirring, until fragrant.
Add the meat and cook until it is just sealed on all sides.
Transfer the pot to the slow cooker (or tip everything into your slow cooker).
Add the rest of the ingredients except the leek and cook on low heat for at least 5 hours or until the meat is tender enough to shred with a fork.
Take the lid off the slow cooker stir through the leek and turn the heat up to high for one hour or until the sauce reduces.
Serve stew with couscous or mashed potato.