Preheat the oven to 190C/375F/Gas 5. Spread out the aubergine slices, pepper quarters and courgette slices in a shallow roasting tin and drizzle with 6 tablespoons of the olive oil. Turn the vegetables until coated and roast in the oven for about 30 minutes or until tender and golden brown.
Meanwhile, in a large frying pan, heat the oil, add the onion and fry gently for 5 minutes. Add the turkey mince, fry until the meat turns pale, then add the tomato pasta sauce and seasoning. Simmer uncovered for 15 minutes, stirring occasionally.
Cook the potato slices in a pan of boiling water until just tender. Drain.
Layer the roasted vegetables and turkey mince in an ovenproof dish and arrange the potato slices over the top. Beat together the ricotta, yoghurt and grated cheddar and spoon over the potato slices to cover completely.
Scatter over the herbs and bake the moussaka in the oven for 30 minutes or until golden brown.