It is popular all over Spain and often served in bars as a tapa and is eaten either hot or cold.
Some people prefer to make it without the onions.
First, heat the oil in a large frying pan and then gently fry the sliced potatoes until almost soft, stirring from time to time so that they don't burn on the bottom of the pan. Add the onion and the green pepper and continue frying until all the vegetables are soft. Drain the vegetables in a colander to get rid of the excess oil. Beat the eggs in a bowl and season with salt and pepper. Add the potatoes, etc.