Beat the egg whites. Stir in salt and approx. 100 ml water and mix well. Leave to rest. Wash trout thoroughly and pat dry. Wash dill and pat dry. Remove coarse stalks.
Wash the lemon and cut into slices. Season fish from inside with salt and pepper and fill with lemon slices and dill. Put baking paper on a baking tray and oil lightly. With 1/3 of the salt form two beds the size of a fish on the baking tray.
Put fish on top. Cover with remaining salt and press down firmly. The fish should be evenly coated with salt. Cook in the preheated oven (electric cooker: 200 °C/ convection oven: 180 °C/ gas: level 3) for approx. 40 minutes.
In the meantime clean the spinach and wash it thoroughly. Drain. Wash, quarter, seed and dice the tomatoes. Peel and chop onion and garlic. Heat the oil in a large, flat pot.
Fry onion and garlic until transparent and add spinach. Steam covered for about 5 minutes. Stir in diced tomatoes and season with salt and pepper. Fry in open pot for another 3 minutes. Remove the trout from the oven and remove the salt lid.
Serve immediately with spinach. Boiled potatoes taste good with it.