Preheat the oven to 350°F.
In a large skillet, heat the olive oil over medium heat.
Add the sliced squash and chopped onion, cooking until the squash is tender, about 10 minutes.
Stir in the salt, black pepper, and garlic powder.
In a large mixing bowl, combine the cooked squash mixture with sour cream and 1/2 cup of the cheddar cheese. Mix well.
Transfer the mixture to a greased 9x13-inch baking dish.
In a separate bowl, combine the crushed crackers, remaining cheddar cheese, Parmesan cheese, and melted butter.
Sprinkle this mixture evenly over the squash mixture in the baking dish.
Bake in the preheated oven for 25-30 minutes, or until the top is golden brown and bubbly.
Let it cool for about 5 minutes before serving.
