Cook the bacon: Preheat oven to 400 degrees F. Line a rimmed baking sheet with foil (for easy clean up). Lay bacon slices in a single layer on the baking sheet. Bake for 12-18 minutes, or until done.
Place bacon between paper towels to absorb grease and let cool. Then, chop into small pieces.
Reduce oven temperature to 350 degrees F.
Grease a 9x13-inch baking dish.
Place hash brown potatoes in the bottom of the baking dish. Arrange in an even layer.
In a large bowl, whisk together the eggs, milk, garlic powder, onion powder, salt and pepper.
Stir 2/3 of the green onions, bacon, cheese into the egg mixture.
Pour the egg mixture over the potatoes in the baking dish.
Sprinkle the remaining 1/3 of the green onions, bacon and cheese over the top of the casserole.
Cover with foil and bake for 50 minutes. Uncover and bake 5-10 minutes more, until eggs are set.