Preheat a large cast iron skillet over medium heat. Add the oil, then add the diced sweet potatoes. Use a wooden spoon to give them a stir to coat them in the oil. Sprinkle them with half the salt, and let them cook, stirring occasionally, for 3-5 minutes.
Next, add the apples and onion, and season them with the pepper and garlic powder. Don't add the rest of the salt just yet, it won't let the onions brown. Give it all a good stir and let it cook for another 5-7 minutes. Stir it occasionally and adjust the heat if needed to avoid burning.
Season with the rest of the salt, stir, and remove from the heat. The hash is done when all of the vegetables are soft and slightly brown and caramelized.
Fry up some eggs in a separate pan if desired, and place them on top of the hash to serve.