Preheat the oven to 425.
Grease a muffin tin well with cooking spray and set aside.
In a medium bowl, mix the hash browns, egg whites, salt, pepper, garlic powder, onion powder and parmesan cheese.
Place about 1/4 cup of the mixture into each muffin tin and press to spread them up the sides slightly.
Spray liberally with cooking spray again and bake for 25-30 minutes until the outside is golden brown.
Remove from the oven and turn on the broiler.
Add about 1 tablespoon of cheese to each muffin tin and add a sprinkling of bacon.
Place them back under the broiler until the cheese melts--about 3 minutes or so. Keep an eye on it!
Remove and allow to sit in the tin 3 or 4 minutes then using a knife or offset spatula loosen the edges and remove to a rack to cool slightly.
Top with sour cream, green onions and a sprinkling of extra salt and pepper if desired.