Preheat your oven to 375°F and grease a 9x13-inch baking dish.
In a large bowl, whisk the eggs and milk together until smooth.
Add the thawed hash browns, cheese, onion, bell pepper, and cooked bacon or sausage if using.
Season generously with salt and black pepper, then mix everything until well combined.
Pour the mixture into the prepared baking dish and spread it evenly.
Bake for 40–45 minutes or until the eggs are set and the top is lightly golden.
Let it rest for a few minutes before cutting—if you can wait that long. Serve warm.