Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking dish.

In a large skillet over medium heat, cook the ground beef and chopped onion until the beef is browned and the onion is translucent. Drain excess fat.

Stir in garlic powder, salt, and black pepper. Remove from heat and set aside.

In a large bowl, combine the frozen hash browns, 1 cup of cheddar cheese, cream of mushroom soup, sour cream, milk, and paprika. Mix well.

Add the cooked beef mixture to the hash brown mixture and stir until fully combined.

Pour the mixture into the prepared baking dish and spread it evenly. Top with the remaining cup of cheddar cheese.

Bake in the preheated oven for 45-50 minutes, or until the casserole is bubbly and the cheese is melted and golden.

Let it cool for 5-10 minutes before serving. Garnish with sliced green onions if desired.