Heat the vegetable oil in a large pot over medium heat. Add the onion, garlic, and ginger, then cook until the onion softens.
Stir in the gochujang and cook for about one minute to release its flavor.
Pour in the vegetable broth, then add the zucchini and soy sauce. Bring the mixture to a simmer.
Add the catfish chunks and tofu cubes. Let everything simmer gently until the fish turns opaque and flakes easily, about 8 to 10 minutes.
Remove the pot from the heat, drizzle the sesame oil over the stew, and scatter the green onions on top before serving.