In a large mixing bowl, whisk together the soy sauce, gochujang, mirin, minced ginger, garlic powder or paste, sesame oil, neutral oil, and light brown sugar until well combined.

Add the thinly sliced flank or skirt steak to the marinade, ensuring each piece is well coated. Cover and refrigerate for at least 2 hours.

Heat a wok or skillet over high heat for 3 to 5 minutes.

Add half of the marinated beef to the pan in a single layer. Sear for about 3 minutes, then stir and cook for an additional 2 to 3 minutes until browned.

Remove the beef and repeat with the remaining beef. Transfer cooked beef to a pre-warmed serving bowl and garnish with sesame seeds.

Serve immediately with boiled rice and fresh vegetables.