What on earth do you consider to be a spanish tortilla that you'd prefer to eat it cold?

In my part of the world (Spain) they are made with eggs, potatoes and salt - often with onions, occasionally with capsicum peppers.

With onions in they are very nice at room temperature. Either with or without the onions they are pretty unpleasant eaten cold. I guess some people will put ketchup on theirs - I think a light dusting of paprika is plenty.