Pour two-thirds of the oil into a large, heavy-based pot and place on a medium–high heat.
Add the onions, fry for five minutes, stirring occasionally, then stir in the garlic, chilli and peppers, and fry for five minutes.
Add the squash and parsnip, and fry for five minutes.
With a slotted spoon, transfer the vegetables to a bowl, leaving as much hot oil in the pot as possible.
Add the remaining oil to the pot and fry the beans, courgette and aubergine for five minutes, stirring occasionally.
Return the other veg to the pot, add the potato, tomatoes, sugar, tomato purée and plenty of salt and pepper, stir, then add enough water to half-submerge the veg.
Cover, leave to simmer gently for 30 minutes, then season to taste.
Heat the oven to 200°C / gas mark 6.
Use a slotted spoon to lift the vegetables from the pot and into a deep roasting tin in which they'll make a layer 2–3 cm thick.
Pour in the liquid and bake for 30 minutes.
At this point the vegetables should be very soft and most of the liquid should have evaporated.
Garnish with coriander, and serve with steamed white rice.