Place the carrots, mange-tout and mini patisson squash in a bowl. Add the oil, season. Place 1/4 of the vegetables in the centre of each sheet of baking paper. Set the fish fillet on top of the vegetables and garnish with the tarragon. Add the white wine, season with salt.
Draw the front and back edges of each sheet together over the fish, make a 1 cm fold and fold over again twice. Tie the right and left ends of the paper with cooking string, but not too close to the fish.
To poach in the oven
Approx. 20 mins. in the centre of an oven preheated to 160°C.