1. Preheat your oven to 230°C/Fan 210°C/Gas 8. Trim and quarter the aubergines lengthways and pop onto a roasting tin, cut-side down. Drizzle over 1 tbsp olive oil and a good pinch of salt and pepper. Slide the aubergines into the oven and roast for 20-25 mins, till the edges are slightly charred and the middles are very soft.
2. While the aubergines roast, finely slice the onion. Halve the chilli, removing the seeds and white pith if you prefer a less fiery dish, and finely chop it. Peel and grate the garlic cloves. Finely chop the coriander stalks (save the leaves for later).
3. Pour 1 tbsp oil into a large pan and bring to a medium-high heat. Slide in the onions and fry for 5 mins, till they start to turn golden brown.
4. Reduce the heat slightly and stir in the garlic, chilli, coriander stalks, and 1 tsp each turmeric, cumin and garam masala, and a little salt and pepper. Cook for 2 mins, stirring frequently.
5. Pour in the chopped tomatoes. Quarter-fill the empty tin with cold water (around 100ml) and stir into the sauce. Bring to the boil, then reduce to a simmer and cook for 15 mins.
6. While the sauce cooks, tip the rice into a sieve and give it a good rinse under cold water. Tip into a small pan and add 300ml boiling water and a pinch of salt. Pop on a lid and bring to the boil, then turn right down and very gently simmer for 8 mins, till all the water has been absorbed. Take the rice off the heat and leave it to steam in the pan, covered, for 10 mins.
7. Grate the lemon zest into the thickened sauce and squeeze in half the juice. Have a taste and add a little more salt if needed.
8. Spoon the sauce into deep bowls and top with roast aubergine wedges and the coriander leaves. Serve with the fluffy basmati rice on the side.