Spanish Omelette Casserole

large onion (chopped)

or 85 g Chorizo sausage (thinly sliced)

or 225 g potatoes (peeled and cubed. King Edward potatoes are the nicest, but any you have to hand will work.)

olive oil

eggs (lightly beaten)

or 110 g grated Cheddar cheese

fresh flat leaved parsley (chopped)

Salt and pepper