• Prepare the vegetables and set them aside.
• Rinse the lentils and discard any debris. Fill a medium pot with plenty of water and add the bay leaf, thyme, and a light sprinkling of salt. Add the lentils to the pot and bring the water to a boil before decreasing the heat to a simmer.
• Cook for about 15 to 25 minutes or until the lentils have just become tender. (Le Puy lentils seem to take a bit longer than other French green lentils.) In the meantime, place a dutch oven over medium heat and add a tablespoon or two of olive oil. Add the red onion, carrot, and celery to the pot. Saute the vegetables, stirring occasionally, for about 10 to 15 minutes or until the onion is translucent. While the lentils are simmering and the vegetables are softening, prepare the dressing.

For the Dressing

• Whisk together the red wine vinegar, dijon mustard, olive oil, walnut oil (if using), and finely chopped shallot. Add kosher salt and freshly ground black pepper to taste.

Assembling the Salad

• As soon as the lentils are tender, drain them and discard the bay leaf and woody remains of the thyme sprigs.
• Add the lentils to the vegetable mixture. While the lentils are still warm, pour over the dressing. Gently stir everything together and let the salad cool briefly.
• Mix the walnuts and parsley into the salad and then serve with the crumbled feta sprinkled over the top.