Thinly slice the mushrooms and put them on a platter.
Mix olive oil, lemon juice, mustard, dry thyme and finely chopped green onions.
Salt and ground black pepper to taste.
Mustard should be grainy, not spicy!
Pour the dressing over the mushrooms and let stand for about 10 minutes.
Sprinkle with crumbled cheese before serving.
Enjoy your meal!