Preheat the slow cooker if necessary; see the manufacturer's instructions. Heat half the oil in a frying pan and fry the aubergine slices in batches, adding more oil as needed until they have all been fried and are softened and lightly browned on both sides. Drain and transfer to a plate.
Add the minced lamb and onion to the frying pan and dry-fry, stirring and breaking up the lamb, until evenly browned. Stir in the garlic and flour, then mix in the tomatoes, stock, spices, tomato purée and a little salt and pepper. Bring to the boil, stirring.
Spoon the lamb mixture into the slow cooker pot and arrange the aubergine slices on top, overlapping. Cover with the lid and cook on low for 8–10 hours.
Make the custard topping. Mix together the eggs, yogurt, feta, nutmeg and spoon over the top of the aubergine. Replace the lid and cook, still on low, for ¾–1¼ hours or until set. Lift the pot out of the housing using oven gloves and brown under a hot grill. Serve with salad.