Anything chow-worthy by Edinburgh airport?
I'm not sure what's available close to the airport, but BAA offers a Paul restaurant (French patisserie/bakery/sandwich spot) and also a seafood bar. There are other chains, too, like E.A.T. If it's a long layover, you're probably best getting into Edinburgh for a decent meal and look-see.
The Airport Express takes about 20-30minutes to get into the centre of town (£6 return). Don't know what I would recommend, especially as I don't know what you mean by 'long layover'.
I've always wanted to try the seafood bar. There's also massage available. And you can sample whisky at the Duty Free.