While the chicken is cooking, make the sauce by whisking together the garlic, brown sugar, soy sauce, sesame oil, ginger, gochujang, crushed red pepper, and pepper together in a small mixing bowl.
3 garlic cloves, ¼ cup brown sugar, ¼ cup soy sauce, 2 teaspoons sesame oil, ¼ teaspoon ginger, ¼ teaspoon crushed red pepper or gochugaru, ¼ teaspoon white or black pepper, 1 teaspoon gochujang