In a heated skillet with a splash of oil, cook sliced onion and minced garlic over medium heat for 2–3 minutes until soft and fragrant.
Pour in chicken stock, then add gochujang, gochugaru, soy sauce, honey, and sesame oil. Stir well and bring to a gentle boil.
Add rinsed rice cakes and simmer for 7–10 minutes, stirring occasionally, until tender. If too thick, add 1–2 tbsp water.
Stir in sliced fishcake and cook for 2 more minutes until warmed through.
Lower the heat and add heavy cream. Stir gently until the sauce turns creamy and pink.
Top with shredded mozzarella. Cover and cook for 2–3 minutes until the cheese is fully melted.
Uncover, sprinkle with chopped spring onion, and serve hot.