In a large bowl, mix together the soy sauce, sesame oil, brown sugar, garlic, and red onion. Stir in the black pepper, red pepper flakes, sesame seeds, leeks and carrot. Mix in the meat by hand to ensure even coating. Cover and let marinate for at least 2 hours or overnight.
Brush the bottom half of a wok with cooking oil, and heat over medium-high heat. Put in all of the meat and marinade at once, and cook stirring constantly. The meat will be cooked after just a few minutes. Remove from heat and serve with rice or noodles. For Korean style fire meat, roll the meat mixture up in a leaf of red lettuce.