Defrost shrimps and spinach separately at room temperature. Melt 40 g fat in a pot. Stir in flour and sweat briefly. Add stock and milk while stirring. Bring to the boil, cook for 3-5 minutes.
Stir in wine and season with salt and pepper. Wash the fish, dab dry and season with salt, pepper and 1-2 tbsp. lemon juice. Peel 1 onion and cut into cubes. Heat 1 tablespoon of fat in a pot and fry the diced onion until transparent, stirring continuously.
Defrosted spinach lightly squeeze, add to the ##onion##, bring to the boil and season with salt, pepper and a little nutmeg. Grease an oven dish (approx. 14 x 23 cm). Put 2 tablespoons of béchamel sauce into the dish and spread.
Place 2 sheets of lasagne on top and spread with 2 tablespoons of sauce. Spread half of the spinach on top. Place 2 sheets of lasagne on top, spread with 2 tbsp. sauce. Lay the salmon on top, first spread with pesto, then with sauce.
Place 2 lasagne sheets on top, spread with sauce and spread the rest of the spinach on top. Spread with sauce. Finish with 2 sheets of lasagne and sauce. Roughly grate the cheese, mix and spread over the lasagne.
Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for 30-40 minutes. Peel prawns, except for the tail fin, and remove the intestines. Wash shrimps and pat dry.
Wash and halve the tomatoes. Peel 1 onion and ##garlic##. Chop onion roughly and slice garlic. Heat the oil and fry the prawns for about 5 minutes while turning.
After about 3 minutes add onion, garlic and tomatoes. Season to taste with salt, pepper and 1 tablespoon lemon juice. Remove the lasagne from the oven, cut into pieces and arrange on plates. Spread the shrimp pan on the pieces.