1. Place the potatoes in a large pot of cold water and bring to a boil. Salt generously. Reduce heat to medium and simmer the potatoes until they are fork tender. Drain and rinse immediately under cold water. Cut the potatoes into 3-cm (1 1/8-inch) rounds and place in a large salad bowl. Add the tomatoes and onions.

2. In a small bowl, whisk together the olive oil, vinegar, salt, pepper and oregano. Reserve a few tablespoons of the dressing, pour the rest over the potato salad and toss gently to combine. To serve, place the sardine fillets decoratively on top of the potato salad and drizzle with the reserved dressing. Serve immediately.