- Peel and cut the potatoes in slices. Place the slices in a pan of cold, salted water. Bring to the boil and cook for 20 minutes. Leave to cool. Drizzle with cider vinegar. Set aside at room temperature.
- Combine the ingredients for the marinade. Cut the tuna into medium-sized cubes. Pour the marinade over the tuna, stir together, and keep in a cool place for 1 hour.
- Cut the radishes into cubes and the cucumber into thin slices.
- Place the potatoes, tuna, radishes, cucumber, and rocket in two large bowls. Pour over a little lime juice.
- Serve garnished with sesame seeds and chives.
Tip: For an extra touch of colour and crunch, add small cubes of beetroot.