Knead a dough from the flour, eggs and salt and leave it under the foil for about 30 minutes. Roll out the dough into a thin crust with a rolling pin or a lasagna machine. The crust is then cut into rectangles. Fry the finely chopped onion, chopped garlic and mushrooms in a pan on the fire for about 5 minutes. Add the chopped spinach, oregano and salt. Fry for another 2-3 minutes, then set aside to cool. Add cottage cheese and mix well to get a homogeneous mixture. Apply a very thin layer of the spinach mixture on the lasagna pan. Arrange the lasagna, then put the filling and grated yellow cheese on them. The procedure is repeated twice more. Finally, pour in the béchamel sauce and grated yellow cheese. Bake at 180 ° C for 20-25 minutes.