Rinse the French green lentils thoroughly under cold running water in a fine-mesh strainer, discarding any small stones or debris. Drain them completely and set them aside while you prepare the vegetables.

Heat the olive oil in a medium saucepan over medium heat until it shimmers. Add the diced onion, carrot, and celery, cooking for 5 to 6 minutes while stirring occasionally until the vegetables begin to soften and the onions turn translucent.

Stir in the minced garlic, fresh thyme sprigs, and bay leaf. Sauté the mixture for about 1 minute until highly fragrant, taking care not to let the garlic brown or burn.

Pour in the rinsed lentils and the vegetable broth, stirring gently to combine all ingredients. Bring the liquid to a boil over high heat, then immediately reduce the heat to low, cover the pot with a tight-fitting lid, and let it simmer.

Simmer covered for 25 to 30 minutes, or until the lentils are tender but still retain a slight bite. Remove the saucepan from the heat, discard the thyme sprigs and bay leaf, and stir in the red wine vinegar.

Season the lentils with the kosher salt and freshly cracked black pepper to taste. Transfer the warm lentils to a serving bowl and garnish with an extra drizzle of olive oil or fresh parsley if desired.