This recipe comes from Rebecca Seal's picturesque cookbook Lisbon: Recipes from the Heart of Portugal. It's a simple dish of fish lightly spiced with bay leaf and garlic, with a strong punch of white wine vinegar.
Heat the oil in a frying pan set over medium heat. Gently cook the fish fillets or steaks for a couple of minutes on each side, until cooked through. Remove and set aside.
Pour the oil from cooking the fish into a small pan, add the onion, salt, and bay leaf and sauté gently over a low-medium heat until the onion is translucent. After about 5 minutes, add the garlic and cook for a further 1-2 minutes. Next, add the vinegar and bring to the boil. Turn the heat down and simmer gently for a couple of minutes.
Remove from the heat and allow to cool a little before adding the parsley. Stir, then pour over the cooked fish. Leave to cool before serving at room temperature; alternatively, the escabeche will keep in the fridge for several days. Taste before serving and add more salt if necessary.