Preheat the oven to 150°C, fan 130°C, gas 2. Place the potatoes with the lamb, onions, cumin, oregano, cinnamon, half of the parsley and all of the stock in a large casserole dish (with lid). Mix well, then layer the tomatoes over the top, season to taste, cover and bake for 3 hours.
Meanwhile, halve the aubergines lengthways and score the flesh in a diamond pattern (taking care not to cut through the skin), then lay on a baking tray. In a small bowl, mix the oil with the crushed garlic and brush over the aubergine flesh.
Turn the oven temperature up to 180°C, fan 160°C, gas 4 and place the baking tray with the aubergines in the oven alongside the casserole for the last 30-40 minutes of the lamb cooking time.
Dust the roasted aubergine with smoked paprika, drizzle with yogurt and sprinkle over mint leaves. Serve the aubergines with the lamb kleftiko, sprinkling the remaining parsley over the lamb.