Heat a pan with cooking olive oil on a medium heat and add the mushrooms. Sprinkle with a touch of salt and pepper and some thyme. Stir occasionally until the mushrooms are cooked.
Crack the eggs into a mixing bowl, add salt and pepper and whisk.
Heat oil in another pan over a medium heat.
When the pan is warm add the egg mixture and swirl it around so it fills the pan. When it starts to set, gently push the sides of the egg towards the middle of the pan and swirl the pan around so the loose egg mixture runs into the gaps.
Now turn the heat right down and add the mushrooms and parmesan to the one half of the omelette and then fold over the other half. Let it rest for a minute so the cheese melts and serve with mustard and fresh herbs of your choice.