In a large pot or Dutch oven, cook the Italian sausage over medium heat, breaking it apart as it browns, about 7-10 minutes.

Add carrots, onion, and celery. Sauté for 3 to 4 minutes until vegetables begin to soften.

Stir in the garlic, salt, pepper, red pepper flakes (if using), oregano, and thyme leaves. Cook for 1 minute, until fragrant.

Add diced tomatoes with juice and chicken broth. Stir in zucchini and lentils, then drop in the bay leaves.

Bring the soup to a boil, then reduce heat to low. Stir, cover and simmer for 45 minutes to 1 hour, or until lentils are tender. You can cook longer to develop the flavors further if you like.

Remove bay leaves before serving. Taste and adjust seasoning as needed.

Garnish with freshly grated parmesan cheese and chopped parsley.