Heat the oil in a large frying pan over a low heat, add the onion and cook, stirring occasionally, for 6–7 minutes until softened. Increase the heat to high and add the speck, garlic and radicchio. Cook, stirring, for 4–5 minutes until the radicchio is wilted and tender. Season with salt and pepper.
Cook the pasta in a large saucepan of salted boiling water according to the packet instructions until al dente. Drain, reserving a ladleful of the cooking water.
Return the frying pan with the radicchio mixture to a low heat and toss in the pasta. Combine well, then add the reserved pasta cooking water and continue stirring until the pasta is well coated and looks silky. Serve immediately with a drizzle of oil.