Making Gratin of Haddock with Zucchini and Tomato involves the following simple steps:

1. Preheat the Oven: Preheat your oven to 375°F (190°C).
2. Sauté Vegetables: In a skillet, heat olive oil over medium heat. Add garlic and sauté for about 1 minute until fragrant. Then, add sliced zucchini and cook for about 5-7 minutes until tender. Season with salt, pepper, and thyme.
3. Layer Ingredients: In a baking dish, arrange half of the sautéed zucchini on the bottom. Place the haddock fillets on top of the zucchini, followed by the chopped tomatoes. Layer the remaining zucchini over the fish.
4. Prepare the Sauce: In a bowl, mix heavy cream with half of the grated cheese. Pour the sauce evenly over the layered ingredients in the baking dish. Sprinkle the remaining cheese on top for a beautiful crust.
5. Bake: Place the dish in the preheated oven and bake for 30-40 minutes, or until the cheese is bubbly and golden brown. Remove from the oven and let it cool for a few minutes before serving.

These simple steps will guide you in creating this incredible dish with ease.