Preheat oven to 350°F (175°C) and grease a baking dish.
In a large bowl combine sliced squash, zucchini, and corn.
Add shredded cheddar cheese, sour cream, eggs, garlic powder, salt, and black pepper.
Mix until all ingredients are evenly combined.
Pour the mixture into the prepared baking dish.
In a small bowl mix crushed crackers with melted butter.
Sprinkle the buttery cracker topping evenly over the casserole.
Bake for 30–35 minutes until the top is golden and the casserole is set.
Let the casserole cool for a few minutes before serving.