Place egg whites and salt into the Thermomix bowl. Whip 4 min/37°C/Butterfly/speed 3. Set aside.
In a hot pan with EVOO, Place onion, mushroom, capsicum, tomatoes and prosciutto. Fry until browning and softened. Season to taste. Set aside.
In a bowl, place the egg yolks, salt and pepper. Whisk up with a fork. Add the egg whites and fold together until combined.
Fill the Thermomix bowl with water to the 1 litre mark. Place Varoma on top. Line the Varoma tray with wet, scrunched up baking paper. Pour half of the egg mixture on to the tray. Steam 12 min/Varoma/speed 4.
Grate parmesan over the omelette, then top one half with prosciutto, cooked vegetables and feta. Fold the omelette over to cover. Steam 5 min/Varoma/speed 4.
Repeat with other half of the egg mixture.