Preheat oven to 375°F (190°C). Grease a 9×13-inch baking dish.
Boil potato cubes for 5–6 minutes until just tender; drain.
Brown ground beef in a skillet; drain fat and season with garlic powder, salt, and pepper.
In a large bowl, combine beef, potatoes, sour cream, milk, and half the cheese.
Pour into dish, top with remaining cheese and bacon.
Bake for 25–30 minutes until cheese is melted and bubbly.
Garnish with green onions and serve.
