In a medium mixing bowl, combine gochujang, gochugaru, soy sauce, sugar, garlic, ginger, and mirin to create the marinade sauce.
Add the chicken pieces to the marinade, tossing to coat thoroughly, and let sit for 15 minutes at room temperature.
Heat the vegetable oil in a large skillet or wok over medium-high heat.
Place the sweet potato slices in the pan and cook for 2 minutes per side until partially softened.
Add the marinated chicken to the pan and stir-fry for 5 minutes until the meat is mostly cooked.
Add the cabbage, onion, and rice cakes to the skillet. Cover with a lid and steam for 5 minutes until the cabbage is wilted and the rice cakes are soft.
Remove the lid and add the green onions and sesame oil.
Stir-fry on high heat for an additional 2 minutes to reduce the sauce and glaze the ingredients before serving.