Cook the gnocchi according to the package directions, reserving 1/4 cup of the cooking liquid.
Meanwhile, heat the oil in a large skillet over medium heat. Add the onion and cook until softened, about 5 minutes. Add the sausage and cook, crumbling it with a spoon, until browned, 5 to 7 minutes. Add the garlic, spinach, salt, and pepper and cook, tossing frequently, until the spinach wilts, about 3 minutes. Add the drained gnocchi, the reserved cooking liquid, and the Parmesan and toss. Divide among individual bowls and sprinkle with additional Parmesan.
Tip: Gnocchi are small, quick-cooking dumplings, usually made from potatoes. You'll find them with the fresh or dried pasta in supermarkets, or you can substitute a short pasta, such as rigatoni, penne, or farfalle.