For the marinade, mix all the ingredients. Cut the swordfish into 2-3 cm cubes, mix with the marinade and leave to marinate overnight, covered and in a cool place.
Remove the seeds from the peppers and cut them into strips. Briefly scald the tomatoes, peel, seed and dice. Peel the potatoes and cut into bite-sized pieces.
Sauté chopped onion and garlic in olive oil. Add bell bell pepper strips and saute for 5 minutes. Add tomatoes and potatoes, season with salt, pepper and paprika powder, cover and simmer on low heat for 2-3 minutes.
Deglaze with white wine and simmer covered for another 30 minutes, adding the vegetable stock.
Remove the swordfish from the marinade and sprinkle with lemon juice. Season with freshly ground salt and pepper. Stir Vin Santo and oregano into the vegetables, add fish pieces and continue steaming for about 5 minutes.
Finally, season again with salt and pepper and serve.