Cut a shallow slit or criss-cross on the top of each tomato and place them in a bowl. Pour boiling water over the tomatoes and leave to stand for 5 minutes. Drain, allow to cool slightly, peel the skins off and roughly chop the tomatoes.
Heat olive oil in a heavy-based frying pan over medium-low heat. Pierce the chilli once or twice with the tip of a knife and add it to the oil.
Separate basil leaves from stalks and finely chop the stalks. Add minced garlic and basil stalks to the oil. Cook, stirring occasionally, over low heat until garlic is soft and fragrant. Do not allow garlic to colour, as it will become bitter.
Add chopped tomatoes, a pinch of salt and pepper and leave to simmer over low heat for 20 to 30 minutes, breaking up tomato with the back of a spoon or a potato masher.
Heat oven to 220°c. Lightly oil a shallow baking dish that is large enough to accommodate your fish fillets snugly.
Meanwhile, bring a pot of water to the boil. Slice the potato into very thin rounds using a sharp knife or mandolin. Put potato slices in boiling water and cook for 5 minutes. Drain, allow to cool slightly, then place in the bottom of the oiled baking dish, overlapping slightly if necessary.
When tomato sauce has reduced, add a splash of red wine vinegar and cook for a further minute or two. Check and adjust seasoning. Spoon the tomato sauce over the potato slices and bake in the oven for 10 minutes.
Remove baking dish from the oven. Scatter olives and half the basil leaves over the sauce. Season fish fillets on both sides with salt and pepper. Place fish on top of the sauce and scatter capers over the fish.
Bake in the oven for about 15 minutes. This will depend on the thickness of your fish. If you are using thinner fillets, check them after 10 minutes by making a small cut in the thickest part of the fillet.
Scatter the remaining basil leaves over the top, and serve with a crisp salad and a glass of riesling or dry rosé.