Put the potatoes in a pan of cold water and cook them until just tender. Drain, rinse under cold water and let them cool.
When the potatoes are cool, peel them, if they are not organic. Cut them into long slices.
Preheat the oven to 180°C.
Finely chop the onion and garlic, then scatter them into a deep baking dish.
Put the tomatoes on top (with the vine), drizzle with half of the oil and the balsamic vinegar. Scatter the dried herbs on top. Also, add the chilli flakes, if used. Season with salt and pepper.
Put the dish in the oven. Cook for 10 minutes, until the tomatoes have burst.
Lightly mash them with a fork, then scatter the fish pieces on top.
Cut the beans into three pieces and scatter these around the fish.
Season with salt and pepper, then drizzle with the remaining balsamic vinegar and oil.
Cover the dish with the potato slices, slightly overlapping each other, then brush them with olive oil.
Grate the cheese over the potatoes.
Bake for 20-25 minutes, until the cheese has melted and the potatoes are golden.
Serve warm.