In a large saucepan over medium, heat the oil until shimmering, then add the fennel seeds; cook, stirring, until fragrant, about 1 minute. Add the sausage and cook, breaking it into small chunks, until starting to brown, 5 to 6 minutes. Add the wine and cook, scraping up any browned bits, until most of the liquid evaporates, about 4 minutes.
Add the onion, celery, carrot, garlic and ½ teaspoon each salt and pepper; cook, stirring occasionally, until the vegetables just begin to soften, about 4 minutes. Stir in the tomato puree and bring to a simmer over medium-high. Reduce to medium-low, cover and cook, stirring occasionally, until the vegetables are tender-crisp and the sauce is lightly thickened, about 25 minutes.
When the ragù is simmering, in a large pot, bring 4 quarts water to a boil. Add the pasta and 1 tablespoon salt, then cook, stirring occasionally, until al dente. Reserve about 1½ cups of the cooking water, then drain and return the pasta to the pot.
Into the ragù, stir the olives and half of the oregano. Add the ragù and 1 cup of the reserved cooking water to the pasta in the pot; stir, adding more cooking water 1 tablespoon at a time as needed if the mixture looks dry. Taste and season with salt and pepper. Serve sprinkled with the remaining oregano and pecorino and drizzled with additional oil.
