Defrost the fish and cut into large cubes. Mash the tomatoes. Clean, wash and slice the zucchini. Peel the vegetable onion and cut into fine slices. Steam vegetables in hot fat.
Deglaze with stock and pureed tomatoes and bring to the boil. Cook deep-frozen soup vegetables for about 10 minutes. Add fish and cook for another 10 minutes. Season to taste with salt, cayenne pepper and vinegar.