Heat oil in large pot over medium-high heat. Add sausage and cook until browned, stirring occasionally, about 5 minutes. Using slotted spoon, transfer sausage to bowl.
Add onion, carrots, parsnips, celery, and Italian seasoning blend to drippings in pot; cook until onion is translucent and vegetables begin to soften, stirring often, about 7 to 8 minutes.
Add lentils; stir to coat. Add 3 quarts broth. Bring to boil; reduce heat to medium and simmer until lentils are tender, about 20-25 minutes. Stir occasionally, adding more broth by 1/4 cupfuls if the soup gets too thick.
Add sausage to soup and simmer until vegetables are tender and flavors blend, about 10 to 12 minutes. Season to taste with salt and pepper. Stir in spinach. Cook until spinach is wilted, about 3 minutes.
Ladle into bowls and garnish with fresh grated Parmesan cheese. Serve with crusty French bread.