Expression
はらがへった
腹が減ったな。この件については、昼飯を食べながら話さないか？
I’m hungry. Would you like to continue this over lunch?
When your belly has decreased in the amount of stuff inside it, you become hungry.
The reading is 腹 plus 減る put together. With these two combined, you have はらがへった.
Sometimes you'll see and hear people use just 腹減った, without the が. Just so you know.