Heat the olive oil in a medium to large pot over medium heat. When hot, add the leeks, carrot and thyme. Stir and  cook for 5 -7 minutes. Then add the garlic and cook another minute.

Add the lentils and the stock and adjust flavorings to taste with salt and pepper.  Bring to a boil and then reduce the heat and simmer for 30 minutes or until the lentils are tender and the water is reduced to your desired consistency. Stir occasionally. Add the parsley and spinach and stir just until wilted.  Transfer to bowl and sprinkle with Parmesan cheese if desired.