Creating Zucchini Gratin is straightforward if you follow these simple steps:

1. Preheat Oven: Preheat your oven to 375°F (190°C).
2. Prepare Zucchini: Wash and slice the zucchinis into thin rounds. Set aside.
3. Mix Cheese and Cream: In a bowl, combine the grated Parmesan, shredded mozzarella, heavy cream, minced garlic, thyme, salt, and pepper. Mix well until blended.
4. Layer Zucchini: In a greased baking dish, arrange a layer of zucchini slices at the bottom.
5. Add Cheese Mixture: Pour a portion of the cheese and cream mixture over the zucchini, spreading it evenly.
6. Repeat Layers: Continue layering zucchini and cheese mixture until all ingredients are used, finishing with the cheese mixture on top.
7. Prepare Breadcrumb Topping: In a small bowl, mix breadcrumbs with olive oil. Sprinkle this mixture evenly over the top layer of zucchini.
8. Bake: Place the baking dish in the preheated oven and bake for 30-35 minutes, or until the top is golden brown and bubbly.
9. Cool: Remove from the oven and let it cool for about 5-10 minutes before serving.
10. Garnish: Sprinkle fresh parsley on top for a burst of color and flavor.

These steps will guide you in creating this incredible Zucchini Gratin effortlessly.