Preheat the oven to 200°C. Slice the potatoes into thin slices (approx. 0.5cm thick) and arrange on a tray lined with baking paper. Drizzle with olive oil and season with salt and pepper.
Roast in the oven for 15-20 minutes or until tender and golden. Add the cherry tomatoes to the tray for the last 6 minutes of baking.
Place the eggs in a pot of boiling water and cook for 5 minutes for soft-boiled or 7 minutes for medium-boiled. Drain and transfer the eggs to a bowl of cold water to cool. Peel and set aside.
Blend the tuna, light yoghurt, and parmesan cheese in a blender until smooth and a sauce-like consistency. Season with salt, pepper, and lemon juice to taste. Set aside.
Thinly slice the radishes and red onions. Cut the eggs in half.
Divide the roasted potatoes, roasted cherry tomatoes, radishes, red onions, capers, rocket leaves, and eggs among four plates. Drizzle the tuna sauce on top and season with additional salt and pepper, if required.
