Cut the onions into thin rings, place in a large pan and fry briefly in the oil. Cut the salmon into strips, add it to the pan with the king prawns and crabs with the onion rings and season with a little salt and pepper. When everything is well seared, add about 100 ml of cream and simmer on a low level. Add the garlic clove. Gradually season with 2-3 tablespoons of curry powder. Sprinkle in the turmeric until the cream has turned a nice yellow color. Season with a little cayenne pepper and black pepper.
Cook the spaghetti al dente and drain. Then add to the pan with the other ingredients and mix well. Now add the rest of the cream and simmer for about 5 minutes.
Divide the spaghetti on two deep plates and add some crème fraîche. Sprinkle with a little cayenne pepper (for the color harmony) and serve.