Instructions:
1. Preheat your oven to 375°F (190°C). Grease a baking dish with butter or cooking spray.

2. In a large skillet, heat the olive oil over medium heat. Add the sliced onions and minced garlic. Sauté for 5-6 minutes, or until the onions become translucent and slightly caramelized.

3. Add the sliced zucchini, yellow squash, eggplant, and red bell pepper to the skillet. Season with salt and pepper to taste. Cook for 8-10 minutes, stirring occasionally, until the vegetables are slightly softened.

4. In a separate saucepan, heat the heavy cream over medium heat until it begins to simmer. Remove from heat and stir in the shredded cheese until melted and smooth. Season with salt and pepper to taste.

5. Transfer the sautéed vegetables to the greased baking dish, spreading them out evenly.

6. Pour the creamy cheese sauce over the vegetables, ensuring they are well coated.

7. In a small bowl, combine the grated Parmesan cheese and breadcrumbs. Sprinkle this mixture evenly over the top of the vegetables and sauce.

8. Place the baking dish in the preheated oven and bake for 25-30 minutes, or until the gratin is bubbly and the top is golden brown and crispy.

9. Once the gratin is done, remove it from the oven and let it cool for a few minutes. Garnish with fresh herbs, such as thyme, rosemary, or parsley, for added freshness and aroma.

10. Serve the vegetable gratin as a delicious main course or as a side dish alongside roasted meats or grilled chicken. It pairs well with a fresh green salad or crusty bread.

Vegetable gratin is a delightful and satisfying evening dish that showcases the natural flavors of a variety of vegetables. With its creamy sauce and crispy breadcrumb topping, this gratin is a crowd-pleaser for vegetarians and veggie lovers alike. Enjoy the comforting and delicious combination of sautéed vegetables, creamy cheese sauce, and crispy golden crust. Whether you serve it as a main course or a side dish, vegetable gratin is a wonderful way to elevate your evening meal with wholesome and flavorful ingredients.