Preheat the barbecue or smoker and bring to 125˚C and add some woodchip 10 minutes before starting smoking to warm up the woodchips.
Place the potatoes in a saucepan and fill with water and a pinch of salt. Brin to the boil and simmer for 20-25 minutes or until cooked through. Drain and keep while the potato cools just enough to handle.
Prepare the potatoes salad by slicing into bit size pieces the warm potato and placing in a bowl.
Add the shallot, spring onion, cherry tomatoes, and coriander. Spoon some crème fraiche and Season with salt and pepper. Stir to combine the flavour and keep aside until needed.
When ready to serve, season the mackerel with salt and pepper and place on the hot barbecue smoker.
Clove the lid and let the fish cook for 4-6 minutes or until the skin can be lifted from the flesh. Serve the mackerel with the potato salad and enjoy hot and at room temperature.