1. Preheat the oven to 350°F (175°C) and grease a casserole dish.

2. Melt the butter in a large sauté pan over medium heat.

3. Add the sliced squash and chopped onion and cook until tender, about 7 minutes.

4. Drain any excess liquid and transfer the cooked vegetables to a mixing bowl.

5. Whisk together the eggs, milk, salt, pepper, and garlic powder in a separate bowl.

6. Stir the shredded cheddar cheese into the egg mixture.

7. Fold the sautéed squash and onions into the creamy cheese mixture.

8. Pour the mixture into the prepared casserole dish and spread evenly.

9. Sprinkle breadcrumbs evenly over the top of the casserole.

10. Bake uncovered for 30–35 minutes until bubbly and golden brown on top.

11. Let the casserole rest for 5–10 minutes before serving.