1. Preheat oven to 350°F (175°C). Grease a 9X13-inch baking dish. Heat a large frying pan over medium heat. Add oil and cook hash browns stirring every 2-3 minutes until golden brown, about 10 minutes. They may take less time if thawed.
2. In a large bowl, mix hash browns and all remaining ingredients except the Parmesan cheese and green onion. Transfer hash brown mixture to the prepared baking dish. Sprinkle Parmesan cheese on top. Bake at 350°F (175°C) for 1 hour. Garnish each serving with fresh green onions.