1. Mix 4 tbsp of the olive oil, thyme, and zest together. Set aside.

2. Boil the potatoes about 25 minutes until tender. Drain, cool, peel, and cut into thick slices. Place in a bowl. Drizzle with the remaining 1 tbsp olive oil, mix with mayonnaise, and season with salt.

3. Heat the vegetable oil in a small skillet over high heat. Fry the capers about 2 minutes, until crispy. Drain on paper towels.

4. Slice the tuna thinly across the grain. Divide the slices among 4 plates. Scatter with capers, sprinkle with salt, and drizzle with olive oil. Add equal amounts of the potatoes to each, and serve immediately.