Cook the duck in a dry frying pan for 3–4 minutes until the fat is released. Remove from the pan using a slotted spoon and keep warm.
Meanwhile, cook the asparagus in a saucepan of boiling water for 2–3 minutes, then drain and halve widthways. Add to the fat in the frying pan and cook for 1–2 minutes until lightly browned, then stir in the radishes and cook for 1 minute.
While the asparagus is cooking, heat a nonstick frying pan over a medium-low heat and dry-fry the walnuts for 3–4 minutes, stirring frequently, until slightly golden. Whisk together the oil and vinegar in a bowl.
Toss together the duck, asparagus and radishes, toasted walnuts and beetroot. Serve drizzled with the dressing.