The phrase "a halved" is correct and usable in written English.
It can be used when referring to something that has been cut into two equal parts.
Example: "I ordered a sandwich, but I only ate a halved portion of it."
Alternatives: "a split" or "a divided".
At lunchtime, spoon into a halved toasted pitta.
Along with your herb of choice, place a halved unpeeled onion, a halved head of garlic, a piece of carrot and a stalk of celery with leaves attached.
It looked like a halved board, since the clubs were sitting so favorably for declarer.
A teacher happily lectures a class mesmerized at the palpable truth of a halved heart.
Serve in sake cups and garnish with a halved (or peeled) black grape, if desired.
Another two followed on the last, meaning a halved match and respective rounds of 63.
City opinion is divided on whether Tesco's new management can reverse a halved share price.
For a mild citrusy flavor, combine halved lemons, a halved onion and bay leaves.
Not a halved hole in that match yet, three wins each.
For my first try at Cata, the bartender gently muddled a halved kumquat at the bottom of a glass.
And some buyers loved parts of his design, he said, like the cap in the shape of a halved orange.
