White Sauce
In a pan, fully melt the butter, add the wheat flour and cook for 1 minute. Stir constantly so it doesn't burn, gradually add the milk and mix. Add the salt and the nutmeg, stir nonstop until slightly thickened.
Making the Filling
In a pan, sauté the onion until translucent, add the garlic and sauté until golden. Add the paprika and the previously cooked and shredded chicken, mix. Add the chopped tomato, the tomato sauce, the salt, the dried parsley, the water and mix it all together very well. Set aside.
Assembly
Into a baking dish, add a layer of white sauce, then add a lasagna sheet, cover it with another layer of white sauce and add a layer of shredded chicken, top it with cheese. Make a second lasagna sheet layer, cover it with white sauce, add the rest of the chicken, the mozzarella cheese, the white sauce, the last layer of lasagna sheet, the last layer of white sauce and top it all with some mozzarella cheese.
Bake in a preheated oven at 180°C (356°F) for 25 minutes.