Get started by slicing your Swiss Brown mushrooms into halves. Heat olive oil or butter in a small oven-safe fry pan over medium-high heat and add the mushrooms, cooking for 6–8 minutes until softened. Turn regularly, until cooked through, golden and caramelised. Remove from the pan and set aside.
In the same pan, reduce the heat to medium-low and add the whisked eggs, cooking while gently lifting and folding the eggs until they begin to set firm, Once they begin to firm up, simply keep the edges loose so the omelette doesn’t stick. While it's still slightly runny on top, add the cooked mushrooms back to the pan, scattered evenly on top of the eggs. Place the pan under the grill until mushrooms are lovely and charred and the eggs are completely set.
To serve, top with some dressed fresh rocket, thinly sliced red onion, dried chilli flakes and a pinch of salt.