Heat the olive oil in a large pot or Dutch oven over medium heat. Add the sausage and cook, breaking it up with a spoon, until browned and cooked through.

Add the onion, carrots, and celery. Cook for 5 to 6 minutes, stirring occasionally, until the vegetables begin to soften.

Stir in the garlic, Italian seasoning, and red pepper flakes, if using. Cook for 1 minute until fragrant.

Pour in the chicken broth and diced tomatoes with their juices. Bring the soup to a boil, then reduce the heat and simmer for 10 to 12 minutes.

Add the gnocchi and cook according to the package directions, usually 3 to 5 minutes, until they float and become tender.

Stir in the spinach and cook just until wilted, about 1 minute.

Reduce the heat to low and stir in the heavy cream. Season with salt and black pepper to taste.

Ladle into bowls and serve hot with grated Parmesan cheese on top.