"荷包蛋只煎一面" can be translated into English as "The sunny-side-up egg is only fried on one side."
Here, "sunny-side-up egg" is a common term for a fried egg cooked only on one side, with the yolk remaining runny. While strictly speaking, "荷包蛋" in Chinese cuisine might refer to an egg cooked in a specific way (often with the egg white wrapped around the yolk, though this can vary by region), in many English-speaking contexts, "sunny-side-up egg" is a widely recognized and understood term for an egg that's been fried on one side only. If you want to be more precise and emphasize the wrapping aspect of the egg white (though this may not be universally recognized in English), you could say something like "The egg is fried sunny-side-up with the white partially enclosing the yolk," but this is more descriptive and less commonly used. The first translation is generally sufficient for most situations.