Whisk the eggs in a pan and add the fried potatoes and onion to it. Pour the mixture in a pan containing a few drops of olive oil, and fry it for a few minutes. Since olive oil is so expensive, I normally fry the potatos and onions with some corn or sunflower oil, and just use the olive oil for cooking the omelette itself. Just those few drops add lots of flavour. You can add some other ingredients to the omelette before frying it.
Red peppers are a common ingredient.
Since I visited Mexico and got a big supply of Mexican chiles I have been adding to my Spanish omelettes 6 dry Serrano peppers, and the result is a very interesting spicy flavour. Just add them when you are frying the potatoes and onions. Take the head of the squid and pull it out carefully, so that it carries with it all the inner organs. Attached to the stomach there is a little black bag which contains the ink. Take it aside, and submerge it in half a glass of red wine.