If using onions and mushrooms- Add the butter to a medium to large size skillet and heat it over medium. Once the butter is melted, add in the onions and mushrooms and saute them for about 5 minutes, until the onions are translucent and both are softened. 

Remove the onions and mushrooms from the skillet and set them aside. Now add the vegetable oil into the same skillet, and add half of the pre shredded hash browns. Now sprinkle the shredded cheddar cheese over the first layer of hash browns. 

Now add the remaining hash browns on top of the shredded cheese, and use a spatula to spread them out evenly and press them down into the skillet as flat as possible. 

Sprinkle the seasonings over the top of the hash browns, including the: seasoned salt, black pepper, and garlic powder. 

Let the hash browns cook for at least 5 minutes, then use a large plate to help flip the hash browns over. Gently place the plate over the skillet, flip the skillet over so that the hash browns turn onto the plate, then slide the flipped hash browns back into the skillet.

Cook the hash browns on the other side for another 5 minutes, or until they are golden brown. Turn off the heat and add your sauteed mushrooms and onions over the hash browns, then place the sliced american cheese on top and allow it to melt. 

Serve right away, and enjoy!