How to cook
Coat the cleaned mackerel fillets with mustard and fill them with with the green spices. Place them in an oven dish, covered with aluminum foil on which you've arranged a 3/4″ (2 cm) layer of sea salt.
Spray the fish with lemon juice. Sprinkle the top with a thin layer of slightly moistened salt and carefully cover it with foil. Bake the mackerel in a preheated oven at 320°F (160 °C) for about 20 minutes.
Then increase the heat to 374°F (190 °C) and bake for another 10 minutes. Finally, roast for 5 minutes without the foil. Serve the roasted mackerel cleaned of the salt.