Heat the oil in a large, heavy-based frying pan, add the peppers, garlic, aubergine and courgettes and cook over a medium-high heat, stirring and tossing occasionally, for 10 minutes until softened and lightly golden in places. Add the tomatoes and cook for 3 minutes. Pour in the wine and measurement water and bring to the boil, then cover and simmer for a further 10 minutes.
Meanwhile, bring a large saucepan of lightly salted water to the boil, crumble in the stock cube with the parsnips and mix well. Bring to a gentle simmer and cook for 10 minutes until the parsnips are tender. Drain well, return to the pan and mash with the soya spread, then stir in the thyme leaves.
Transfer the ratatouille mixture to a large gratin dish. Spoon the mashed parsnips over the vegetables and season generously with pepper. Bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 20 minutes until the top is lightly golden in places. Serve with a simple green salad.