Crack the eggs into a bowl and add splash of milk, and some seasoning and beat gently.
In a frying pan over a medium heat, warm a little oil and add the bacon, onion, mushrooms (and any other uncooked ingredients if substituting). Remove from the pan and set aside.
Add a knob of butter to the frying pan and increase the heat to medium high and wait until it is sizzling. Gently pour in eggs and reduce to a medium heat. When the omelette is semi-set, throw in your cooked and other fillings and cover with lid - this helps to cook the omelette and evenly melts any cheese you are using. Alternatively you can pop under the grill for a minute to help cook the top.
Gently shake the pan to loosen the omelette and slide onto a plate. Flip over one half (as in the photo!). Add whatever favourite condiment, grab a fork and enjoy!