Pre-heat the oven to 180°C. Prepare a large frying pan into which all of the salmon portions will fit in one go. Heat the dry pan on a medium heat, place the fillets skin side down and fry for around 2 minutes. Turn them then carefully with a spatula and cook on the other side for a further minute and a half.
Bring a pan of water to the boil for the pasta. Meanwhile finely chop the onions, mince or purée the garlic, and rince the spinach in cold water. Tear any larger leaves of spinach. Cook the tagliatelle al dente, checking regularly as it gets close to the bite.
Take the salmon out of the pan and lay in a casserole dish. Leave the pan on the hob and heat a tablespoon of oil. Add the onions to this and sauté for around one minute on a medium heat. Then turn down the heat and add the puréed garlic and, right after, the spinach. Cook this for four minutes on a low heat. Finally, pour in coconut milk, season with salt and pepper, and leave to stew together for 3 minutes.
Pour the resultant mixture into the casserole dish over the salmon fillets and put in the oven for 7-8 minutes at 180°C.
Serve the salmon and sauce over a nest of tagliatelle and, finally, sprinkle some dill over it.