Preheat your oven to 375°F (190°C).
In a large bowl, combine ground beef, breadcrumbs, egg, chopped onion, and minced garlic. Season with salt and pepper.
Transfer the meat mixture into a greased baking dish, pressing it evenly across the bottom.
In a separate bowl, combine diced potatoes, sour cream, milk, and half of the shredded cheese. Mix until well combined.
Spread the potato mixture evenly over the meatloaf layer.
Sprinkle the remaining shredded cheese on top of the potato layer.
Bake in the preheated oven for 45 minutes or until the top is golden and bubbly.
Remove from the oven and let it cool for 10 minutes before serving. Garnish with chopped green onions.