Heat the oil in a large saucepan over medium-high heat.
Add the pork belly (in batches) and season generously with sea salt and freshly ground black pepper.
Cook the pork belly (in batches) until it has browned nicely.
If the pork belly has produced a lot of fat, remove some fat from the pan, if necessary. Otherwise, you will need a few tablespoons of fat/oil in the pan for the rest of the recipe.
Add the onions and cook until softened.
Add the kimchi, together with all of the juices from the kimchi packet or container. Cook for a few minutes until warmed through.
Add the stock and bring everything to a gentle simmer.
Add the Gochujang, chilli flakes, salt and sugar.
Simmer gently for 15 to 20 minutes.
Taste for seasoning. If the soup needs more salt, consider adding a dash of fish sauce.
Add the sliced tofu and cook for a few minutes until the tofu has warmed through. Take care not to break the tofu.
Garnish with spring onions (scallions).
Serve with steamed rice.