Preheat oven to 350°F. Grease a 9x13 inch baking dish.

In a large pot, boil sliced squash and diced onion for 5 minutes. Drain well and pat dry with paper towels.

In a large bowl, mix together cooked squash, onion, cheddar cheese, sour cream, cream of chicken soup, beaten eggs, 2 tablespoons melted butter, garlic powder, salt, pepper, and parsley.

Pour the mixture into the prepared baking dish.

In a separate bowl, mix crushed crackers with 1/4 cup melted butter and Parmesan cheese.

Sprinkle the cracker mixture evenly over the squash mixture.

Bake for 30-35 minutes, until the top is golden brown and the casserole is bubbly.

Let stand for 5 minutes before serving.