In a large skillet or pot over medium heat, cook the sausage until browned. Drain excess fat if needed.
Add diced onion and cook until softened, about 3 minutes. Stir in minced garlic and cook for 1 minute.
Pour in diced tomatoes, chicken broth, heavy cream, Italian seasoning, salt, and pepper. Stir well and bring to a simmer.
Add the gnocchi and cook according to package directions, usually about 5 minutes, until tender.
Stir in fresh spinach and Parmesan cheese until the spinach wilts and the sauce is creamy.
Serve immediately, garnished with extra Parmesan if desired.