When buying the fish, ask your fishmonger to gut and scale it, but do not remove head and tail. At home, rinse the fish under fresh water and then pat it dry with kitchen paper.
Cut a large piece of foil so that you can wrap your fish later. In the centre of the foil put a layer of greaseproof paper, roughly of the same length as your fish. Put some drops of olive oil on the greaseproof paper.
Spread the olive oil all around the greaseproof paper (use your fingers or a little brush).
Slice the potatoes (thin slices) and lay the slices down like shown in the picture. Then, drizzle some olive oil over the potato slices. The potato helps to absorb part of the liquid that may form in the bottom during the cooking.
Take the fish and season its belly starting with a drizzle of olive oil.
Then, season the belly with salt and black pepper.
Put half of the capers inside the fish gills.
Next, stuff the belly with a third of the olives and tomatoes (cut in half). With the remaining tomatoes, capers and olives, spread them on top and around the fish. Drizzle with olive oil over the fish.
Season the outside with salt.
Season the outside with black pepper.
Close the wrap, seal it folding the sides and put it onto an oven tray. Pre-heat the oven to 200°C (400°F). When the oven is hot, put the tray into the oven and cook the fish for about 35 minutes.
Once the fish is cooked, remove the top skin and drizzle with some good quality olive oil (the fish may be served on the wrap).