Ham and Cheese Hash Brown Casserole

Ingredients:

1 bag (30 oz) frozen hash browns, thawed
2 cups cooked ham, diced
2 cups shredded cheddar cheese
1/2 cup shredded mozzarella cheese
1 small onion, finely chopped
1/4 cup butter, melted
1 can (10.5 oz) cream of chicken soup
1/2 cup sour cream
1 teaspoon garlic powder
1/2 teaspoon onion powder
Salt and pepper to taste
1/2 cup crushed cornflakes or breadcrumbs (optional for topping)