Preheat the oven at 200 degrees Celsius.
Cut the sausages in round slices.
Cut the paprika, carrots, zucchini, and the onion in small pieces.
Fry the sausages in olive oil together with the vegetables and the tomato sauce. Add the soy sauce and let it boil on low temperature for 5 minutes.
Cut the feta and mozzarella cheese.
In a casserole melt the butter, add the flour and mix. Add the milk and let it boil while stirring. Add the salt and pepper and stir together. Put on the side.
Butter an oven form and cover the bottom with lasagna plates.
Put half of the sausage mixture over the lasagna plates. Sprinkle half of the feta cheese on top. Repeat with another layer. Put a final layer of lasagna plates on top. Pour the rest of the white sauce on top and add the mozzarella as a last layer.
Place in the middle of the oven for 30 minutes.