Preheat the oven to 200 ° C fan-assisted air. Peel the potatoes and onions and cut into fine strips. Season with marjoram or oregano, salt and pepper. Put 4 tablespoons of olive oil in a baking dish and turn the vegetable mixture well. Bake on the middle shelf for about 30 minutes, turning more often.
In the meantime, wash the fish fillets, pat dry and season with salt and pepper. Take the vegetables out of the oven, smooth them out and cover with the fish fillets. Brush with a little olive oil and pour the white wine over it. Bake at 160 ° C for about 10 minutes. Squeeze the garlic cloves and mix with parsley and breadcrumbs. Add so much olive oil until you have a spreadable mass. Brush the fish evenly with it and bake in the oven at 180 ° C until it is brown and crispy.
It goes well with stewed vegetables such as ratatouille or courgette pan or simply salad.