Preheat oven to 350°F (175°C) and grease a baking dish.
In a bowl mix ground beef, breadcrumbs, egg, milk, diced onion, garlic powder, salt, and black pepper.
Press the meat mixture evenly into the bottom of the baking dish.
Bake for 20 minutes until the meatloaf base begins to cook.
Remove from the oven and spread mashed potatoes evenly over the meat layer.
Sprinkle shredded cheddar cheese and crumbled bacon on top.
Return to the oven and bake another 20 minutes until cheese melts and becomes bubbly.
Garnish with chopped green onions before serving.