Making Cheesy Potato Breakfast Casserole is straightforward when you follow these steps:

1. Preheat Oven: Preheat your oven to 350°F (175°C).
2. Prepare Baking Dish: Grease a 9×13-inch baking dish with cooking spray or butter.
3. Mix Hash Browns: In a large bowl, combine the frozen hash browns with half of the cheddar cheese and half of the mozzarella cheese.
4. Spread Hash Brown Mixture: Evenly spread the hash brown mixture into the prepared baking dish.
5. Whisk Eggs: In another bowl, whisk together the eggs, milk, garlic powder, onion powder, salt, and pepper until well combined.
6. Add Meat and Veggies: Stir in the diced ham or bacon and bell peppers, if using.
7. Pour Egg Mixture: Pour the egg mixture over the hash brown layer in the baking dish.
8. Top with Cheese: Sprinkle the remaining cheddar and mozzarella cheeses on top.
9. Bake: Place the casserole in the preheated oven and bake for 45-50 minutes or until the eggs are set and the top is golden brown.
10. Cool Slightly: Allow the casserole to cool for about 5-10 minutes before slicing.
11. Garnish: Top with chopped green onions if desired.

These simple steps will guide you in creating this incredible breakfast casserole effortlessly.