Preheat oven to 190°C. In a bowl mix together the breadcrumbs, Parmesan, Gruyère, garlic, basil, caraway seeds and oregano, set aside.
In a pan, add the butter and sauté the onions over a moderate heat until soft. Griddle or grill the courgette slices for a few minutes on each side.
In a greased gratin dish, add the onions and tinned tomatoes and arrange the courgettes in layers on top with a coating of the cheese, bread and herb mixture between each layer. Top with the breadcrumb mixture and bake in the oven for 30 minutes until brown and crisp.
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Freezing and defrosting guidelines
In order to enjoy optimum flavour and quality, frozen items are best used within 3 months of their freezing date. Always defrost and heat thoroughly before eating. For more tips on freezing and defrosting food, read our article Love Your Freezer.