Line slow cooker with a disposable liner and spray with non-stick spray.
Layer frozen hash browns, bacon, onions (if using), and 1 cup shredded cheese in the crock pot in two or three layers.
Sprinkle the remaining 1-2 cups shredded cheese over the top evenly.
Beat the eggs, milk, dry mustard, Susie Q, salts, and pepper together.
Pour the egg mixture over the cheese evenly in the crockpot.
Cook on low for 7 to 8 hours or until eggs are set and thoroughly cooked.