If using bacon or sausage, cook and crumble. Drain fat leaving 1 tablespoon in the pan.
If desired, soften the onion in the fat. This is optional but will soften the flavor of the onion.
Grease a 6qt slow cooker. Place half the hash browns, meat, onions, peppers, and cheese in the slow cooker. Repeat layers ending with cheese, do not stir.
Whisk eggs, milk, and seasonings in a medium bowl. Pour the egg mixture over the ingredients in the slow cooker.
Cook on low for 7 to 8 hours or high for 3-4 hours. Once cooked, uncover and let the casserole rest for 15 minutes.
