Add several Tbsp. of oil to a large nonstick skillet on medium-high heat until the . Add the raw onion and cook, stirring occasionally until the onion starts to turn faintly translucent with tinges of brown.
Add the chunks of corned beef and potatoes. Continue to fry on medium-high heat, turning and stirring the hash frequently for about 10 minutes. If the food starts to stick, add more oil. You can also turn down the pan to medium if it is too hot.
Add the cabbage and grind in some black pepper. Continue to cook until everything is hot through and the beef and potatoes are as crispy as you would like. About 5-10 more minutes in total.
Taste for salt and add some if needed. If your veggies were cooked in the corned beef juices you may have enough salt already.
Serve hot with fried eggs.