Heat olive oil in a large skillet over medium heat. Add sausage and cook until browned, breaking it apart with a spoon.
Add diced onion and cook until soft, about 3 minutes. Stir in garlic and cook for 30 seconds until fragrant.
Pour in diced tomatoes, chicken broth, heavy cream, and red pepper flakes. Stir well and bring to a simmer.
Add the gnocchi and stir to combine. Cover and let simmer for 5-7 minutes, or until the gnocchi is tender.
Stir in mozzarella, Parmesan, and spinach. Cook until cheese melts and spinach wilts.
Season with salt and pepper to taste. Serve hot and enjoy!