In a large, deep skillet, heat the oil over medium heat. Once it's hot, add the sausage. Cook until it's mostly browned, breaking it up as you go, then add in the onion and continue to cook until the onion has softened up, about 3-4 more minutes. Add the garlic and cook just a minute or so more, until fragrant. Then add the tomatoes, gnocchi, cream, broth and seasonings and give it all a good stir.
Let it come up to a simmer, then let it simmer for 6-8 minutes, or until the gnocchi are tender and the liquid has absorbed and thickened a bit. Remove it from the heat and immediately stir in the spinach, then the mozzarella cheese. Once the spinach has wilted, you are ready to serve.
