Place lentils in a large bowl. Cover with boiling water, and allow to rest for 15 minutes.
Drain the lentils and set aside.
In a large stockpot, sauté the onions, leeks, and garlic in the olive oil over medium heat. Add the thyme, cumin, salt, and pepper. Cook for 20 minutes or until the vegetables are tender and translucent.
Add the celery and carrots and sauté for another 10 minutes.
Add the vegetable stock, tomato paste, and lentils. Cover and bring to a boil.
Lower the heat and allow the soup to simmer, uncovered, for about one hour until the lentils are fully cooked.
Taste and adjust seasonings. Then, add the red wine vinegar.
Serve hot with a sprinkle of parmesan cheese, and enjoy!