Roast the toast slices and brush with creme fraiche.
Cut the onions into cubes and fry in a pan. Add the minced meat to the onions and fry everything well. Pour the tomatoes on top and sprinkle with Italian herbs. Let everything simmer a little. To taste.
Place the toast slices on a prepared baking tray or in a baking dish and distribute the minced meat mixture on top. Place mushrooms on top of the minced meat mixture. Cover with cheese and place in the oven at 200 ° for 15-20 minutes and bake until the cheese has the desired brown color or has melted well.
After gratinating, arrange 2 slices of toast on each plate and serve.