1. Put a little butter in a pan and sauté the onions until translucent and even a little more. Add water when they start to burn. Season with garlic powder, salt and pepper.
2. Put a large pan on medium heat and sprinkle it lightly with salt and pepper.
3. Place the sliced mushrooms all over and do not touch for about 5 minutes and then delicately turn them. They should be a nice golden brown. They shrink quite a bit, but the tastes increase tremendously.
4. Toast the bread.
5. Butter the bread (if you wish) and spread Le Grand cheese onto it.
6. Layer the onions followed by the mushrooms and the parsley. Serve and enjoy!