Preheat the oven to 350˚ F. Spread the walnuts on a baking sheet and bake until toasted, about 10 minutes. Finely chop.
Bring a large pot of salted water to a boil. Meanwhile, heat 1 tablespoon butter in a large skillet over medium-high heat. Add the sausage and cook, breaking up the meat with a wooden spoon, until well browned, 4 to 5 minutes. Remove the sausage to a bowl.
Add 1 more tablespoon butter to the skillet. Add the onion and cabbage and cook, stirring, until the cabbage is wilted, about 5 minutes; season with salt and pepper. Add 1 cup hot water (from the pot) and cover the skillet. Reduce the heat to medium and simmer until the cabbage is tender, about 5 minutes. Uncover, increase the heat to medium high and cook until the skillet is dry, 2 to 3 minutes. Stir in the sausage to reheat, about 1 minute. Keep warm on low heat.
Meanwhile, add the gnocchi to the boiling water and cook as the label directs. Using a slotted spoon, transfer the gnocchi directly to the skillet; add 1 cup cooking water and the remaining 1 tablespoon butter. Increase the heat to medium high and simmer until the sauce is thickened, 2 to 3 minutes, adding more cooking water as needed to loosen.
Divide the gnocchi among bowls. Top with the chopped walnuts, Parmesan and parsley.