Cook the gnocchi according to the package directions. Drain, reserving ¼ 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 gnocchi, the reserved cooking liquid, and the Parmesan and toss. Divide among individual bowls and sprinkle with additional Parmesan.