Cook the lentils in 1⁄2 l salt water covered for 8-10 minutes.
Clean and wash the leek, cut it in half lengthwise and cut it into thin strips. Cut bacon into pieces. Heat oil in a frying pan. Fry the bacon until crispy. Take out, drain on kitchen paper.
Sauté the leek in the frying fat for about 5 minutes. 1⁄8 Add l water, vinegar, stock and thyme, bring to the boil and simmer for 2-3 minutes. Season with pepper and possibly salt.
Drain the lenses. Add to the leek with the bacon and mix well. Season again with salt and pepper. Crumble feta cheese over it. Garnish with thyme. The salad tastes hot or cold.
It goes well with toasted brown bread.