Break the eggs into a bowl and add the water, then season with a pinch of salt and plenty of pepper and beat lightly with a fork.
Heat a non-stick frying pan over a medium heat and then add the butter to melt. Tip in the spinach and cook for 1 minute until wilted. Tip on to a plate until needed.
Quickly wipe out the pan with kitchen roll and then place back on the hob on a medium to high heat. Add the olive oil, swirling it around the sides, then pour in the egg mixture.
Give the egg mixture a quick stir and then start drawing the egg in from the side of the pan with a fork letting the runny egg fill the gaps, go around the pan once doing this.
Scatter over the herbs, wilted spinach and feta on top of the omelette, season with black pepper, carefully fold over a third of the omelette over the middle then the other third to enclose the filling.
Slide the omelette out of the pan and cut into two portions, then arrange on plates with the salad to serve.