For the filling, toss the aubergine slices in the vegetable oil, then drain and season, to taste, with salt and freshly ground black pepper.
Heat a frying pan over a medium heat, add the aubergine slices in batches and fry for 2-3 minutes on each side, or until golden-brown on both sides. Remove from the pan with a slotted spoon and set aside to drain on kitchen paper.
Add the onion, pepper and garlic to the pan and fry for 2-3 minutes, or until softened.
Add the tomato purée, stir to coat the vegetables in it, then continue to fry for a further 4-5 minutes.
Add the canned chopped tomatoes and cinnamon stick and simmer for 4-5 minutes.
Add the lentils and return the fried aubergines to the mixture. Simmer for a further 2-3 minutes, or until warmed through.
Transfer the mixture to an ovenproof dish and sprinkle over the chopped parsley.
For the topping, in a bowl, beat together the ricotta, Greek-style yoghurt, eggs and grated nutmeg until well combined. Season, to taste, with salt and freshly ground black pepper.
Pour the topping mixture into the ovenproof dish on top of the filling. Sprinkle over the grated parmesan.
Transfer the veggie moussaka to the oven and bake for 25-30 minutes, or until the topping is golden-brown and has set and the filling is bubbling. Serve immediately.