Preheat the oven to 190°C/fan 170°C/gas 5.
Use a small, sharp knife to cut through all the skin and tendons around the ankle of each duck leg. Press each duck leg bone towards the thigh as if holding pliers and cut through the tendon at the prominent leg-thigh joint. This helps the meat to relax when cooking. Rub a little sunflower oil into the duck legs and season with the dried thyme and 1 teaspoon of sea salt.
Put the duck legs on a small baking tray or in a small, ovenproof frying pan and place them into the oven for 1¼–1½ hours, or until they are crispy-skinned and the meat is totally tender to the push of a knife point.
Put the cucumber into a colander and mix in the remaining sea salt. Leave to drain over the sink for 30 minutes. When ready, wring out the cucumber with your hands to extract as much excess water as possible.
In the meantime tip the seeds into a small saucepan and jostle them around over a medium heat until a faintly toasted smell comes to the nose. Now add a dash of sunflower oil to the seeds, followed by the onion, and sweat over a medium heat for 3 minutes or so. Stir in the turmeric and cook for a further minute before adding the remaining ingredients. Simmer rapidly for 2 minutes, then transfer to a bowl and allow to cool.
When the vinaigrette is cool, add the cucumber and stir thoroughly. Leave to sit for at least 10 minutes.
Remove the duck from the oven.
Spread the cucumber over a serving plate and arrange the crispy duck legs on top.