Place the courgettes, aubergine and onion in a large roasting tin and toss with 3 tablespoons of the olive oil. Place in a preheated oven, 220°C (425°F), Gas Mark 7, for 20 minutes until tender and lightly charred in places.
Meanwhile, heat the remaining tablespoon of oil in a large, heavy-based frying pan and cook the onion and garlic over a medium-high heat, stirring frequently, for 3 minutes until softened. Add the tomatoes and cook, stirring occasionally, for a further 10 minutes. Add the tomato purée, herbs and measurement water and bring to the boil, then reduce the heat and simmer for 5 minutes.
While the sauce is cooking, bring a large saucepan of lightly salted water to the boil and cook the fusilli for 10–12 minutes until just tender, then drain.
Add the roasted vegetables to the tomato sauce along with the drained pasta and toss well together. Serve in warmed serving bowls, with warm crusty bread, if liked.