Peel, wash and slice the potatoes. Peppers clean, wash and cut into thin slices. Bring the stock to the boil. Cook the potatoes for about 15 minutes. Cook the pepper strips for about 3 minutes.
In the meantime, wash the fish and pat dry. Season with salt and sprinkle with lemon juice. Roll up the fish and wrap it first in cling film, then in aluminium foil. Steam in boiling water for 10-12 minutes.
Take the fish out, remove from the foil and cut in half. Mix sea salt with 2 teaspoons of olive stock and drizzle over the fish. Season potatoes and peppers with salt and pepper. Arrange on a plate with the broth and the olives.
Place the fish on top and garnish with marjoram. Sprinkle with black pepper.