Bring water to a boil in a medium saucepan; add some salt and lemon juice. Clean the mushrooms, take the stem off and boil them in the water until they are al dente.
Beat the eggs, add the cream and season with salt and pepper. Heat the butter in a frying pan; heat the egg mixture on a medium heat by stirring it gently (scrambled eggs). Fill the mushrooms.
Cut the courgettes in 12 slices, season with salt and pepper, then grill them on both sides in hot olive oil. Arrange 3 slices on a plate, put on top a slice of Zwieback and a stuffed mushroom. Garnish with beetroot sprouts.