Preheat your oven to 375°F (190°C).
In a skillet over medium heat, sauté the onion in oil or butter until soft.
Add ground beef and cook until browned. Drain excess grease.
In a large bowl, mix the soup, milk, garlic powder, and half of the cheese.
Stir in the hash browns and cooked beef mixture. Season with salt and pepper.
Spread the mixture evenly into a greased 9x13-inch baking dish.
Top with remaining cheese.
Cover with foil and bake for 30 minutes. Uncover and bake an additional 10-15 minutes, until golden and bubbly.
Let rest 5 minutes before serving.