Crack the eggs into a small bowl. Add the milk and season with salt and pepper. Whisk until combined.
Melt the butter in a non-stick saucepan over medium heat. Pour in the egg mixture and swirl to cover the base of the pan. Cook for 1 minute then use an egg flip or spatula to pull some of the set egg towards you and let the uncooked egg cover the pan. Cook for a further 2 minutes or until the omelette is almost set. Fold over one half of the omelette and transfer to a plate. Serve with rocket leaves dressed with a little extra virgin olive oil.
Once the eggs have cooked for 1 minute and are almost set, scatter one half with the cheese, mushrooms and parsley. Use an egg flip to fold over half to cover the filling. Cook for another minute or until the cheese starts to melt.
Using an egg flip, transfer the omelette to a plate. Scatter with the extra parsley to serve.