Preheat oven to 400 degrees F. Spray a casserole dish with nonstick cooking spray.
Wash the potatoes to remove any dirt. Cut the smaller potatoes into quarters and the larger ones into six pieces.
Season the potatoes with garlic powder, onion powder, oregano, salt, and black pepper. Mix the potatoes to make sure they're all seasoned.
Bake the potatoes for 30 minutes.
Add the cooked chicken breast to the potatoes. Top with the reduced-fat Mexican cheese and place it back in the oven for 10 minutes, or until the cheese melts.
Once the casserole is done baking top it with the cooked bacon, green onions and fat-free sour cream.