In a small bowl, combine the oregano, cumin, salt, sugar, garlic, lime juice, oil and paprika.
Place the chopped onions on the bottom of a slow cooker and place the lamb on top so it's not touching the sides of the bowl.
Pour over the spice mix and the chopped tomatoes and then add the cinnamon stick, bay leaf, cloves and chopped chili on top.
Put the lid on and cook on low for 8 hours.
Take the lid off and spoon the juices over the lamb. Put the lid back on and cook on high for half an hour.
Carefully remove the lamb to a serving platter.
Serve it with tortillas and your choice of accompaniments.