Preheat the oven to 350°F (175°C).

In a large skillet, melt a little butter over medium heat. Sauté the sliced squash and chopped onion until softened, about 5 to 7 minutes.

In a mixing bowl, combine the cooked squash mixture with the beaten eggs, milk, salt, pepper, and half of the shredded cheese.

Grease your casserole dish with butter or cooking spray.

Pour the squash mixture into the prepared casserole dish and spread it out evenly.

In a separate bowl, mix the crushed crackers with the melted butter and sprinkle this mixture over the squash.

Place the casserole in the preheated oven and bake for 25 to 30 minutes until the top is golden brown and the casserole is bubbly.

Remove the casserole from the oven and let it sit for about 10 minutes before serving.