Rinse the mackerel fillets, pat them dry and sprinkle them with salt on both sides. Put them head to toe in a stainless steel dish. Cover with cling film and leave in the fridge for 3 hours.
At the end of this time, rinse the fillets and then soak them for 1 hour in cold, lightly salted water.
Rinse the radishes and cut them into thin slices, using a mandolin. Let them rest in iced water.
Peel the onion and cut it into thin slices with a mandolin.
Drain the mackerel fillets, rinse and pat dry; remove the bones with tongs, then peel the skin from the head with a sharp movement, lift it up and pull it towards the tail: it is very easy to remove. Then cut the mackerel fillets into 2 cm wide strips.
Drain the radishes and divide them into four plates with the onions.
Add the mackerel and wrap the raspberry vinegar and lemon squeezed oil droplets around them. Sprinkle with chilli and serve.