Add the onions, garlic, tomato puree, lamb, chopped tomatoes, red wine vinegar, courgettes, sweetener, cinnamon, oregano, bay leaf, salt and pepper to the slow cooker and stir well.
Cook on high for 3 to 4 hours or medium for 6 to 7 hours.
If the sauce seems a little watery, remove the liquid and continue to cook until the liquid has reduced slightly.
Slice the aubergine lengthways, spray with low calorie cooking spray, then place on a baking tray and grill until they are starting the soften. Turn them over and do the same on the other side.
Next make the white sauce. In a bowl, mix together the yogurt, eggs, mustard powder and a pinch of salt and pepper. Set aside.
Pre-heat the oven to 180°C.
Place a layer of the lamb mix on the bottom of an oven proof dish.
Top with a layer of grilled aubergine then another layer of the lamb mixture.
Top with a final layer of aubergine.
Pour the white sauce over the top, making sure there are no gaps.
Sprinkle the grated cheese evenly over the top, then cook for 30 – 40 minutes, or until the cheese is golden brown.
Remove from the oven and allow to stand for a few minutes before serving.