Marinate the beef: In a bowl, combine soy sauce, brown sugar, gochujang, garlic, ginger, salt, and pepper. Add the beef and marinate for 15 minutes.
Cook the beef: Heat oil in a skillet over medium-high. Add the beef and cook for 3-4 minutes per side until caramelized. Set aside.
Make gochujang mayo: Mix mayonnaise with 1 tsp gochujang in a small bowl.
Assemble tacos: Warm tortillas in a dry skillet. Fill each with beef, cabbage, green onions, and a drizzle of gochujang mayo. Sprinkle sesame seeds and serve with lime wedges.