In a large pot, cook the sausage over medium heat until browned and cooked through. Remove the sausage from the pot and set aside.
In the same pot, add the diced onion, carrots, and celery. Sauté until the vegetables are soft, about 5-7 minutes.
Add the minced garlic and cook for an additional minute until fragrant.
Add the lentils, diced tomatoes, broth, thyme, oregano, and bay leaves. Bring the mixture to a boil, then reduce the heat and simmer for about 30 minutes or until the lentils are tender.
While the soup is simmering, slice the cooked sausage into bite-sized pieces.
Once the lentils are tender, remove the bay leaves and add the sliced sausage and chopped kale to the pot. Simmer for an additional 5 minutes until the kale is wilted.
Season with salt and pepper to taste.
Serve hot, garnished with grated Parmesan cheese if desired.