Preheat your oven to 400°F (200°C). Place the cubed potatoes in a large pot and cover with water. Bring to a boil and cook until tender, about 15-20 minutes. Drain and return to the pot.
Add sour cream, milk, melted butter, garlic powder, onion powder, salt, and black pepper to the potatoes. Mash until smooth and creamy.
Stir in 3/4 cup of cheddar cheese, crumbled bacon, and green onions until well combined.
Transfer the potato mixture to a greased 9x13-inch baking dish and spread it evenly.
Top with the remaining 1/4 cup of cheddar cheese.
Bake in the preheated oven for 25-30 minutes, or until the cheese is melted and bubbly.
Let cool for a few minutes before serving.