Prepare the ingredients: cut the Chicken Thighs into bite-size pieces; core and thinly slice the Green Cabbage; peel and slice the Sweet Potato into 1/4-inch rounds or half-moons; slice the Onion into wedges; trim and slice the Scallion on the diagonal; if frozen or hard, soak the Tteok (Korean Rice Cakes) in warm water for 10–20 minutes to soften; stack and thinly slice the Perilla Leaf for garnish.
Make the sauce: in a bowl whisk together the Gochujang, Gochugaru, Soy Sauce, Rice Wine, Sugar, Corn Syrup, minced Garlic, grated Ginger, a pinch of Black Pepper and a splash of Sesame Oil until smooth and glossy.
Toss the chicken in most of the sauce (reserve a couple of tablespoons for finishing) and let it sit for 15–30 minutes if you have time — this helps the flavors penetrate.
Heat a large, heavy skillet or cast-iron pan over medium-high heat and add a couple tablespoons of Neutral Oil. When shimmering, add the sweet potato and onion and cook, stirring occasionally, for 3–4 minutes until they begin to soften and color.
Push the vegetables to the side and add the marinated chicken in a single layer. Let it sear undisturbed 1–2 minutes, then stir to combine with the vegetables. Cook for 4–5 minutes more until the chicken is mostly cooked through.
Add the sliced cabbage and the softened tteok to the pan, pour in any remaining sauce, and toss everything together. Reduce heat slightly and continue to cook, tossing occasionally, until the cabbage wilts, the tteok becomes chewy and warmed through, and the sauce thickens and glazes the ingredients (about 4–6 minutes).
Taste and adjust seasoning — add a little more soy or sugar if it needs balance — and finish with the reserved sauce if you want extra heat and gloss.
Turn off the heat and stir in the sliced Scallion and scatter the Perilla Leaf on top. Drizzle a touch more Sesame Oil if desired and sprinkle with Sesame Seeds to garnish.
Serve hot from the pan, ideally with steamed rice and banchan; let diners wrap bites in lettuce or enjoy straight from the skillet.
