Preheat oven to 200ºC/180ºC Fan/Gas Mark 6. Heat the olive oil in a large sauté pan and add the aubergine.

Cook for 8 minutes on a medium–high heat, stirring occasionally, until golden-brown. Remove with a slotted spoon to kitchen paper and set aside. Add the carrot and celery to the pan and fry for 8 minutes. Transfer to kitchen paper. Reduce the heat to medium and add the onion and garlic. Cook for 5 minutes, stirring often. Add the orzo and tomato purée and cook for a further 2 minutes.

Remove the pan from the heat and pour in the stock, fresh oregano or thyme and lemon zest. Add the cooked vegetables, mozzarella, Parmesan, 1 teaspoon of salt and ½ teaspoon of pepper. Mix well and transfer to a rectangular ovenproof dish, 21cm x 27cm, or a round one, 27cm in diameter. Arrange the tomatoes on top and sprinkle with the dried oregano, along with ¼ teaspoon of salt and a grind of pepper.

Bake in the oven for 40 minutes, or until all the liquid has been absorbed and the pasta is cooked through. Remove from the oven, leave to settle for 5 minutes and serve.