In a large ovenproof sauté pan or frying pan, heat the olive oil over a medium-low heat and sweat the onions and garlic (with a pinch of salt) for around five minutes until soft and translucent.
Next, add the herbs before stirring through the chopped tomatoes. Add seasoning and then the chopped red peppers. Simmer (uncovered) on medium-low for around ten minutes.
Meanwhile, slice your three veggies into rounds of about 1cm thickness. If you have a mandolin, this will make the cutting of the courgettes and aubergines especially straightforward and uniformly, the tomatoes are best hand-sliced with a sharp knife. Lay each vegetables’ slices in separate piles on a tray.
Heat the oven to 180ºC and when the sauce is ready, take a slice each of tomato, courgette and aubergine, put them together and place in the sauce, then repeat in a circle/spiral formation with these trio combinations until the pan is full. Brush the tops with some olive oil and place the pan in the oven (uncovered) for around 30-35 minutes until the veggies are tender.
Alternatively, instead of cutting the veggies into slices, you can cut into chunks and place into the base sauce then simmer over a low heat on the hob for around half an hour until tender and serve.