Cut the chicken tenderloin into bite-sized pieces.
Slice onion, carrot, and cabbage into thin strips.
Make the marinade by mixing gochujang, soy sauce, sugar, minced garlic, chili powder, sesame oil, and pepper.
Add the marinade to the chicken tenderloin and vegetables, then mix and let it marinate for 10 minutes.
Add cooking oil to a pan and preheat over medium heat.
Add all the chicken and vegetables to the pan and stir-fry.
When the chicken is cooked through and the vegetables are tender, it's done.