Chop the onions finely, then braise them. Add the mince and paprika to them. The mince needs to braise well. After it is, add the olives and mushrooms to it. Add the salt and black pepper. Braise everything briefly. Then add the tomato juice. Leave to boil until the sauce thickens.
Preparing the Bechamel Sauce:
Melt the butter and braise the flour in it. Next, add the milk and stir energetically nonstop. Season the sauce with salt and black pepper. Leave to boil until the sauce thickens.
Put water in a pot to boil with a little oil. Once boiling, remove from the stove. Submerge the lasagna sheets, 1 by 1, in the water for 1-2 min. each, to prevent sticking. Smear the tray with oil. Arrange a layer of lasagna sheets, then sauce with mince and a little Bechamel sauce. Keep arranging in this order until out of products. Finish off with lasagna sheets. Pour on the remaining Bechamel sauce.
Grate the cheese over the lasagna. Bake in a preheated 392°F (200 °C) oven for about 40 min.