Prepare the lentil garnishes first; heat the vegetable oil in a saucepan over a moderate heat and sweat the onion and garlic for 4-5 minutes, stirring occasionally. Add the drained lentils, stir well then add the spices. Cover with the vegetable stock and bring to the boil. Reduce to a simmer and cook for 20-25 minutes until soft. Remove from the heat and adjust the seasoning to taste. Reserve to one side to reheat later.
Prepare the raita by mixing together the yogurt, cucumber and mint in a mixing bowl until smooth. Cover and chill until needed. Cook the potatoes in a large saucepan of boiling, salted water until tender; roughly 15-20 minutes.
Meanwhile, heat the sunflower oil in a large saucepan over a medium-high heat until hot. Sauté the aubergine chunks until lightly coloured, then remove from the saucepan. Reduce the heat a little and add the onion, poppy seeds and chilli, sweating for 4-5 minutes, stirring occasionally, until the onion has softened. Add the garlic, all the spices, the bay leaf and 1 tsp of salt and stir well. Cook for 1 minute, then add the aubergine back to the saucepan.
Drain the potatoes when ready, allow to steam for 1 minute, then add to the saucepan along with the curry leaves. Add 300ml of water, bring to a simmer and cook, covered, for 10 minutes until the potato is just breaking down. Adjust the seasoning after 10 minutes then remove the bay leaf and spoon into a metal serving dish.
Preheat the grill to medium-hot. Reheat the rice and the lentils and spoon into serving dishes to sit alongside the curry. Warm the chapati under the grill at the same time and spoon the raita into a serving dish as well. Serve alongside the curry.