Preheat the oven to 400°F. Line a half-sheet baking pan with parchment paper.
Into a large bowl, add the frozen hash browns and onions. Drizzle with butter and toss to coat.
In a small bowl, combine the salt, black pepper, and garlic powder. Sprinkle over the hash browns and toss again to evenly distribute the seasonings.
Transfer to the prepared baking sheet and spread into an even layer.
Bake for 45 minutes, or until hashbrowns reach your desired level of crispness. Serve hot.