Peel the onion and chop finely. Rub the peel off the lemon and then squeeze the lemon.
Heat 1 tablespoon of oil in a saucepan and sauté the onions in it. Add the frozen spinach and water and simmer over medium heat for about 10 minutes.
Rinse the thawed salmon or saithe, pat dry and dice. Heat 1 tablespoon of oil in the pan and fry the fish in it for about 4 - 5 minutes. Season with salt and pepper and remove.
Heat the butter in the frying fat and fry the gnocchi in it for about 6 - 8 minutes until golden brown. Also season with salt and pepper.
Now stir the lemon zest, lemon juice and sour cream into the spinach and season with salt, pepper and nutmeg. Mix in the fish and gnocchi and briefly heat everything together again.