For the filling: heat the oil, sauté the onion and garlic. Add zucchini, mushrooms and tomatoes, steam for about five minutes. Add oregano, steam briefly, season, set aside.
For the sauce: warm the butter. Steam flour while stirring with whisk at medium temperature until soft, flour should not take color. Remove skillet from heat. Add milk all at once, stirring to bring to a boil, reduce temperature, season. Gently simmer sauce over medium heat, stirring occasionally, for ten minutes until creamy. Add cheese, stir well.
Lasagna: pour a quarter of the vegetable filling into the prepared mold, place three lasagna sheets on top, mold a quarter of the cheese sauce on top. Continue like this until the whole is used up, finish with cheese sauce. Sprinkle with parmesan cheese.
Bake in the middle of the oven heated to 200 °C for about thirty minutes.
Serves with: mixed salad
Tip: Zucchini are a type of pumpkin and therefore low in calories, rich in vitamins and easy to digest – just the thing for a light meal!