Place the beef in a large bowl. Add chopped garlic cloves and onion. Season with pepper and pinch of salt. Follow with soya sauce, mirin and sugar. Mix all well making sure that whole beef is covered in sauce.
In a large frying pan (or a wok) preheat 1 tbsp of olive oil. Place beef into the pan and cook on medium heat until beef is starting to brown a little. Once done add chopped spring onion and mix it through. Cook for another 2 min.
Done! Serve with freshly cooked rice and a side of kimchi or sriracha and enjoy!