In a large bowl, combine the ground beef, low-sodium soy sauce, sesame oil, gochujang, brown sugar, garlic, ginger, onion, cornstarch, and green onions and mix well. Let marinate and sit in the fridge for at least 20 minutes.
Heat oil on a frying pan over medium high heat. Add in the marinated beef and stir-fry for 3 minutes or until cooked thoroughly while breaking the beef into smaller pieces using a spatula. Remove from heat and set aside.
Marinated Cabbage
In a large bowl, combine the shredded cabbage, rice wine vinegar, and granulated sugar and mix well. Set aside.
Spicy Gochujang Mayonnaise
In a small bowl, combine the Japanese mayonnaise, gochujang, and sesame oil and mix well. Set aside.
Assembling the tacos
To prepare the corn tortillas, heat a flat-bottomed pan over medium high heat. Toast the corn tortilla for 1-2 minutes on each side or until slightly golden. Remove from heat and set aside.
To assemble the tacos, lay the corn tortillas flat and add the shredded cabbage. Place the cooked beef on top of the bed of cabbage and top with the spicy mayonnaise and green onions.