- In a saucepan, bring all the ingredients, except for the cucumber, to a boil. Add the cucumber slices and remove from the heat. Cover and marinate for 1 hour. Drain.
- Preheat the grill, setting the burners to medium.
- Lay a square of parchment paper in the centre of a large, double sheet of aluminum foil. Place half the cucumber slices in the centre of the parchment paper, arranging them to cover about the same surface area as the fish. Place the fish on top of the layer of cucumbers. Season with salt and pepper. Top with the remaining cucumber slices. Close and tightly seal the papillote.
- Place the papillote on the grill and cook for about 12 minutes, depending on the thickness of the fish, or until the fish is cooked through.
If you prefer, you can also grill the fish in individual papillotes. In this case, reduce cooking time accordingly.