recipe for squash casserole

Ingredients 4 cups sliced yellow squash (about 4 medium squash) 1 small onion, finely chopped 1 cup shredded cheddar cheese 1/2 cup grated Parmesan cheese 1/2 cup mayonnaise 1/2 cup sour cream 2 large eggs, beaten 1/2 teaspoon salt 1/4 teaspoon black pepper 1/4 teaspoon garlic powder