Preheat oven 200°C. Lightly grease a baking tray. Place the mushrooms, stalk side up on a tray. Dot 40g of the butter evenly over the mushrooms. Season with salt and pepper. Bake for 10 minutes or until mushrooms are just tender.
Meanwhile, whisk the eggs with a fork until well combined. Season with pepper.
Melt half the remaining butter in a 20cm (base) non-stick frying pan over medium-low heat. Pour in half the egg mixture, tilting the pan until the egg covers the base. Sprinkle with half the parmesan and cook for 3-4 minutes or until just set. Fold the omelette in half and slide onto a plate. Cover and keep warm. Repeat with remaining butter, egg and parmesan.
Cut the omelettes in half and divide between serving plates. Top with mushrooms and season with salt and pepper. Serve with toasted bread.