Heat oil in a large (5- to 7-qt.) Dutch oven or other heavy pot over medium-high. Add sausage, and cook, breaking up with a wooden spoon, until it begins to brown, about 4 minutes.
Add garlic and cook, stirring often, until softened, 2 minutes. Stir in pasta, marinara, and water. Bring to a boil over medium-high. Cook, stirring often, until pasta is al dente, 10 to 12 minutes.
Add kale and salt, stirring constantly to combine, until kale is wilted, about 1 minute. Serve with grated cheese, if using.