Preheat the oven to 200°C/fan 180°C/gas mark 4. Place the courgettes, aubergines, peppers and sliced red onion on a large roasting tray. Toss in 1 tbsp olive oil and roast for 30 minutes, turning halfway through until just cooked and golden brown.
Meanwhile, bring a large pan of water to the boil. Heat ½ tbsp olive oil in a medium saucepan and cook the diced red onion for 5 minutes, until slightly softened. Add the garlic and cook for a further 1 minute. Add the chopped tomatoes, oregano, tomato purée and balsamic vinegar and simmer for 20 minutes, until thickened. Remove from the heat and leave to cool slightly.
Cook the spaghetti for 7 minutes, until it still has a slight bite. Drain and mix with the slightly cooled tomato sauce and roasted vegetables, then stir through the beaten eggs.
Grease a non-stick 20cm springform cake tin with the remaining ½ tbsp oil. Transfer the spaghetti mixture to this and smooth the surface with the back of a spoon, then top with 15g parmesan. Place in the oven for 30 minutes, until crispy and golden on top. Carefully remove from the tin and top with the rocket, halved cherry tomatoes and remaining parmesan before serving.