1. Wash mackerel fillets and drain. Place them on the tray. Sprinkle kosher salt on both sides. Coat well and let it rest for 10 minutes.
2.meanwhile making the sauce
In a bowl, add all the sauce ingredients and mix well. Set aside.
3. Dry the fish with a kitchen towel. Cut in half and slice an "X" on the skin side.
4. In a frying-pan, heat 1/2 tbsp vegetable oil over medium-high heat and wipe off any excess oil with a kitchen towel.
5. Place mackerels (skin side down) onto the frying-pan. Cook about 5 minutes over medium-low heat. Then, flip them and cook for another 3 minutes. Pour the sauce in one go. Flip once to coat the fish with the sauce.