"荷包蛋只煎一面" can be translated into English as "The sunny-side-up egg is only cooked on one side."
Alternatively, you could also say:
"The fried egg is cooked sunny-side-up (only one side is fried)."
"The egg is fried only on one side, making it a sunny-side-up egg."
The term "sunny-side-up" is commonly used in English-speaking countries to describe an egg that is fried on one side only, with the yolk remaining runny and the white fully set.