Cook onions in butter and saffron until they are tender. Add sugar, rhubarb, toasted sunflowers seeds, vinegar and water and cook for 5mins, then season. The liquid should be acidic enough to pickle because it will be the solution to finish cooking the mackerel, as in with ceviche.
Dust the mackerel skin with salted flour and once your pan is hot, pan fry the mackerel skin side down until golden and crispy. Make sure that the mackerel skin is as crispy as possible!
Next, put all the mackerel in 2 trays skin side up and add the onion and saffron mix on top. Make sure that all the mackerel fillets are covered with this mix otherwise they will not cook through. Leave for 2-4 hours
Cook the prepped mussels in the garlic and white wine in a large saucepan, tossing it thoroughly at intervals until all the mussels open. Leave to cool slightly and then pick the muscles out of their shells.
Chop the seaweed and add in cold pressed rapeseed oil and black pepper to make a salsa.