Cook the lasagne sheets in boiling salted water for 5-7 minutes until al dente.
Peel and finely dice the onion and garlic. Heat the oil in a pot. Sauté onion and garlic in it. Add frozen spinach and 5-6 tablespoons of water. Cover and simmer over medium heat for about 15 minutes.
For the horseradish cream, wash the orange with hot water, dry and finely grate half of the rind. Squeeze the orange. Mix cream cheese, eggs, orange juice and peel, season with salt and pepper.
Remove the lasagne sheets with a skimmer. Quench cold on a sieve and place them next to each other on a tea towel. Simmer spinach open for 3-5 minutes until the liquid has evaporated.
Season to taste with salt, pepper and nutmeg. Wash the fish, dab dry and cut into 8-10 strips. Season with salt and pepper.
Preheat oven (electric cooker: 200°C/circulating air: 175°C/gas: level 3). Spread a little cream in an ovenproof dish. Put 1 lasagne sheet halfway in each, cover with some spinach and 2-3 salmon strips.
Add 2-3 tablespoons of cream. Fold the lasagne sheet over the filling and continue until all the ingredients are used up, while still wrapping the lasagne packs.
Cut the cheese into slices and spread the rest of the cream on the lasagne sheets. Bake in a hot oven for about 25 minutes. Garnish with cress.