In a bowl whisk together eggs, chopped parsley and set aside.
Heat pan over medium heat. Add olive oil and once it starts to sizzle, add onions and potatoes and cook until tender for about 10 minutes, but do not brown.
Once done, turn off heat and cool for few minutes. Next transfer onions and potatoes to the bowl* and combine with egg mixture. Stir in salt and mix to combine.
Heat same pan over medium heat. Pour the egg mixture into the pan and cook until edges begin to set. Then, reduce the heat to medium-low, cover the pan, and cook for 7–8 minutes, or until the bottom is firm and golden brown.
To flip the omelette, place a large plate over the pan and invert it onto the plate. Slide the omelette back into the pan to cook the other side. Reduce the heat to low, cover, and cook for another 2–3 minutes.
Once the bottom of omelette is firm and golden brown, transfer onto a serving plate and let cool. Serve at room temperature or chilled.
Notes
*Make sure to leave enough olive oil in the pan to cook the omelette properly.