In a medium bowl, pop in the beef slices along with the marinade (soy sauce, mirin, sesame oil, garlic, sesame seeds and salt & pepper to taste).
150 g sizzle steak, 2 tbsp soy sauce, 2 tbsp mirin, 1 tbsp sesame oil, 1 tbsp garlic, ½ tbsp sesame seeds, Salt and pepper
While that marinates, bring the water to a boil in a wok. Add in the rice cakes and boil until they are soft and float (around 2-3 minutes, extra if frozen). Drain and transfer rice cakes into a small bowl. Pour over the soy sauce and sesame oil and mix.
1 L water, 250 g Korean rice cakes (tteok), 1 tsp soy sauce, 1 tsp sesame oil
In the same wok, heat the vegetable oil over a medium to high heat. Add the carrot and onion and fry for 2-3 minutes. Next add in the marinated beef and fry for a minute or two until mostly browned. Add in the marinated rice cakes, capsicum, shiitake mushroom, and green onion. Continue frying for another minute or two, then turn off the heat and serve immediately.
1-2 shiitake mushrooms, 1 capsicum / bell pepper, 1 carrot, 1/2 onion, 1 tbsp vegetable oil, 3 spring onion / green onion