Place the salmon fillets on a cutting board or a plate skin up. Using a paper towel press against the skin to remove any moisture. Leave the salmon to rest for 15 minutes at room temperature.
Meanwhile, make the salsa - In a bowl add in the mango, coriander, chilli and onions. Cover the bowl and place it in the fridge until ready to use. For the dressing, in a small bowl use a teaspoon to dissolve the sugar in the fish sauce and lime juice. Leave the dressing to the side for later use.
Just before cooking the salmon use a paper towel once more to remove any moisture of the skin. Turn the salmon and season it with salt and pepper, on the skin side apply a generous amount of salt but no pepper as it will burn.
In a frypan on medium to high heat pour enough to coat the entire base of the pan. Heat up the oil, it will be ready when it sizzles when the salmon touches the oil. Make sure the heat is not too high or it will burn the skin before the salmon is cooked.
Carefully place the salmon in the pan skin down and leave to cook on this side for most of the cooking time. You can determine how far the salmon is cooked by looking at the sides of the salmon, you will see it change colour slowly from the skin upwards. As soon as it's cooked to how you prefer to eat your salmon, flip it over and cook the other side for a minute or so.
Finish off the salsa by gently mixing in the dressing with the mango, taste and add seasoning to suit your taste. Lay the salmon down on a plate with the skin facing up and top it with the mango salsa.