Heat 2/5 cup (100 ml) of oil in a large pan and fry the chopped onion, pepper and 2 cloves garlic. Chop or grate the potatoes into fine slices and add them to the pan.
While they fry, mash the remaining garlic, add 3 1/3 tbsp (50 ml) olive oil and stir with the chopped parsley. Season the mixture with salt and pepper.
Add the spices to the vegetables and transfer everything to a baking tray. On top, distribute the 4 fish fillets, coat them thoroughly with a mixture of garlic, olive oil and parsley.
Arrange the tomato circles, pour on a little olive oil, a little salt and put the dish in to bake for about 20 minutes in a moderately preheated oven.