Place the zucchini slices, cherry tomatoes, and diced red onion in a large bowl.

Drizzle with olive oil and add oregano, basil, thyme, salt, and black pepper.

Toss until the vegetables are evenly coated with seasoning.

Spread the vegetables onto a baking sheet in a single layer.

Roast for about 18–20 minutes until the vegetables begin to caramelize and release their aroma.

Transfer the roasted vegetables to a baking dish and gently spread them into an even layer.

Stir the minced garlic and lemon juice into the vegetables while they are still warm.

Sprinkle the Parmesan and mozzarella evenly over the top.

In a small bowl, combine the panko breadcrumbs and chopped parsley.

Scatter the breadcrumb mixture across the casserole.

Bake for 15–18 minutes until the cheese is melted and the topping turns golden brown.

Allow the casserole to rest for 5 minutes before serving.

Garnish with additional parsley if desired and serve warm.