Preparing Hash Brown Egg Casserole is straightforward and can be done by following these steps:

1. Preheat Oven: Preheat your oven to 350°F (175°C).
2. Sauté Vegetables: In a skillet, heat the olive oil over medium heat. Add the chopped onion and bell pepper, cooking until softened, about 5 minutes.
3. Mix Ingredients: In a large bowl, combine the frozen hash browns, cooked vegetables, ham (or sausage), garlic powder, salt, and pepper. Mix until well combined.
4. Prepare the Egg Mixture: In another bowl, whisk together the eggs and milk until fully blended. Season with a little more salt and pepper if desired.
5. Assemble the Casserole: Grease a 9×13-inch baking dish. Spread the hash brown mixture evenly in the dish. Pour the egg mixture on top, ensuring it covers the hash browns completely.
6. Add Cheese: Sprinkle the shredded cheddar cheese evenly over the top of the casserole.
7. Bake: Place the casserole in the preheated oven and bake for 45 minutes, or until the eggs are set and the top is golden brown.
8. Cool Slightly: Allow the casserole to cool for about 5-10 minutes before slicing. This step will help it hold its shape better when served.
9. Serve: Cut into squares or rectangles, and serve warm.

Following these steps ensures a delicious Hash Brown Egg Casserole that everyone will love!