Soak sea mustard in cold water to remove the salty taste.
Cut beef into bite-sized pieces.
Heat sesame oil in a pot and stir-fry the beef.
When the beef is cooked, add the sea mustard and stir-fry together.
Pour in 500ml of water and bring to a boil.
Add soybean paste and minced garlic, then continue to simmer over medium heat.
Taste and adjust seasoning with Korean soy sauce if needed.
Add green onion, bring to a gentle boil once more, then turn off the heat.