Any of the above, plus a dab of orange marmalade and a sprinkling of lime juice on the finished article, just before I put the last thing into my omelette - a fork!
Whatever I have around. My grandad used to make a great omelette with cream, onions, tomatoes, peppers and other things I can't remember. It was so thick you could cut it into wedges to eat.
A basic Spanish omelette is just with potatoes (grated or sliced), onions and black pepper...plus the attentions of a rather lovely spanish girl and a bottle of vino tinto
Nice additions include combinations of peppers, chillies, mushrooms, beansprouts, sliced sausage (or even small chipolatas/hot dogs whole), broccoli, tomatoes, sweetcorn, baby sweetcorn, courgette, tuna, celery, small meatballs, cooked chicken, chopped ham, peas, green beans, broad beans, gherkins, leeks, cheese and of course paprika or curry powder
Trying to introduce a bit of BR's multicultural lifestyle to Spanish cuisine
One thing I love to do with omelettes (whatever the "fixins") is to make em large and fluffy. I heard this called the souffle omelette but I just think of them as fluffy ones!
Separate yolks from whites - mix your ingredients of choice and seasoning in to the yolks, whisk the whites to stiff peaks, fold the whites into the yolk mix (without losing too much of the fluff if possible) and then add to heated oil in fry pan, using a fork to drag the mixture from the edge of the pan to the centre until it begins to set to ensure it cooks evenly. When the omelette is nearly set, use a fish slice to fold it in half and serve!!
P.S. you gotta be sure no yolk splits into the whites otherwise they won't "fluff up"... so if a yolk does split I just revert to a regular omelette!!
Whatever I have, but favourite is potato, onion, mushroom and pepper (all pre-fried) with some tomato, garlic, a few herbs and cheese in the egg mix, which must be made with milk. Start cooking the mix and then add the potato, onion etc, cook it until solid most of the way through then fold and serve with granary bread - should have a runny middle. Mmmmmmm...