For the mozzarella mushroom toast, halve the onion and cut into fine strips. Clean the mushrooms and cut them into slices. Wash, dry and slice the tomato.
Fry the onion strips in a pan with hot oil, once they have taken on some color, add the mushrooms and fry them as well. Season with salt and pepper.
Meanwhile, cover the toast slices with tomato slices and mozzarella slices on top and bake in a preheated oven at 160 °C until the cheese has melted.
Spread the mushrooms on the toasts and sprinkle with the herbs.