Preheat and Prep: Preheat your oven to 200°C (fan 180°C). Line two large baking trays with baking paper. In a large bowl, toss the aubergine, courgette, bell pepper, and red onion with the olive oil, salt, and pepper until everything is evenly coated. You should hear a soft sizzle as the oil coats the vegetables; they will look glossy and smell wonderfully earthy.

Roast the Vegetables: Spread the seasoned vegetables in a single layer across the two trays. Roast for 25-30 minutes, turning the pieces halfway through, until they are tender and have taken on a lovely golden-brown colour. The edges of the aubergine should be slightly crispy, and the peppers will smell sweet and smoky. Remove from the oven and set aside.

Make the Tomato Sauce: While the vegetables roast, place a medium saucepan over a medium heat. Add the sliced garlic and a splash of olive oil, stirring for about 30 seconds until it becomes fragrant but not browned. Pour in the chopped tomatoes and tomato purée, then add the oregano and thyme. Bring the sauce to a gentle simmer; you will see small bubbles breaking the surface. Let it cook for 10 minutes, stirring occasionally, until it thickens slightly and the colour deepens to a rich, rusty red.

Layer the Casserole: Spread a thin layer of the tomato sauce over the bottom of a 9x13 inch baking dish. Arrange half of the roasted vegetables evenly over the sauce. Spoon half of the remaining tomato sauce over the vegetables, then scatter half of the mozzarella and half of the Parmesan on top. Repeat the layers with the rest of the vegetables, the remaining sauce, and the rest of the mozzarella and Parmesan. The top should look like a patchwork of white and red with green flecks from the herbs.

Bake to Golden Perfection: Place the dish in the preheated oven and bake for 20 minutes, uncovered. At this point, the sauce should be bubbling vigorously around the edges. For a beautifully browned top, switch the oven to the grill setting for the final 3-4 minutes. Watch it carefully; the cheese will turn a deep golden brown and the edges of the casserole will be charred in spots, creating a beautiful, restaurant-quality crust. The sound of the bubbling sauce and the sight of the molten cheese are your cues that it's ready.

Rest and Garnish: Remove the casserole from the oven and let it rest on a wire rack for at least 10 minutes. This crucial step allows the layers to set, making it much easier to serve neat, clean portions. Just before serving, tear the fresh basil leaves and scatter them over the top. The vibrant green against the golden cheese is a stunning final touch. The aroma at this point is deeply savoury and herbaceous.