Prepare a quick mushroom cream soup by stewing the chopped onion and sliced mushroom on the olive oil, adding the water, chicken stock, and cream. When the mushrooms are cooked, put the soup base into the blender and blend it until it's smooth.
Melt the butter in a saucepan and stew the cut green bean on it for 5 minutes.
Put the green beans into a casserole form with the melted butter.
Mix the mushroom cream soup with the salt, pepper, and chopped parsley.
Pour the mixture onto the green beans.
Bake the casserole in the oven at 220°C for 20 minutes until the mushroom sauce starts to be sticky and creamy and the top of the dish starts to harden.