Slice the zucchini and eggplant: Sprinkle both with a little salt and set aside for about 10 minutes. This helps to remove excess moisture and reduce bitterness, especially from the eggplant.

Blanch the broccoli: Bring a pot of water to a boil, and add the broccoli florets. Let them blanch for about 1-2 minutes, then immediately transfer them to a bowl of ice water to retain their bright color and crunchiness. Drain and set aside.

Sauté the vegetables: In a large skillet, heat a drizzle of olive oil over medium heat. Add the chopped red onion, bell peppers, and minced garlic. Sauté for 5-7 minutes until soft and lightly golden.

Prepare the tomatoes: Chop 3 tomatoes and set them aside for later layering in the gratin.

Combine breadcrumbs with seasoning: In a bowl, mix the breadcrumbs, grated Parmesan cheese, rosemary, minced garlic, and a pinch of salt and black pepper. This will create the crispy, savory topping for the gratin.

Prepare the Mozzarella: Shred the mozzarella and set it aside for layering on top of the vegetables.

Layer the vegetables: Preheat the oven to 180°C (350°F). In a large baking dish, start by placing a layer of zucchini slices on the bottom, followed by the eggplant, blanched broccoli, and sautéed onions and bell peppers. Then, add a layer of chopped tomatoes and sprinkle some fresh basil over the top.

Top with Mozzarella: Once the vegetables are layered, sprinkle the shredded mozzarella cheese evenly over the top.

Add the breadcrumb mixture: Spread the breadcrumb-Parmesan mixture evenly over the mozzarella layer. The breadcrumbs will turn crispy as the gratin bakes, creating a delightful crunchy texture.

Arrange tomato slices: Place the 3 small tomato slices on top for decoration.

Drizzle with olive oil: Before placing the dish in the oven, drizzle the top with a bit of olive oil to help the breadcrumbs and cheese brown.

Bake: Bake the gratin in the preheated oven for 25-30 minutes or until the top is golden brown and crispy, and the vegetables are tender.

Finish with fresh herbs: Once out of the oven, sprinkle freshly chopped dill and drizzle the lemon-garlic olive oil dressing over the top for added flavor.

Let the gratin cool slightly before serving. Garnish with additional fresh basil or dill if desired. Enjoy as a main dish or a side with a fresh salad or crusty bread.