Steps
1. Heat a pan on medium-high heat. Add some oil if desired.
2. Add the beef slices to the pan and cook for 1 minute.
3. Add the Ketchup, Mirin and soy sauce and let it simmer for 2-3 minutes.
4. Add the scallion and onion and stir.
5. Add a little sugar if desired.
6. Serve hot.