You might be able to find some good food at the Sheraton or Hilton at Schiphol. Both are within walking distance. The Sheraton is a covered/enclosed walk and the Hilton requires a short distance (a hundred or so yards) outdoors.

I can't vouch for the quality of the food, but I'd expect it to be somewhat better than in the airport proper.

I agree with pbarnette...I don't think you'll have enough time to get to and from downtown Amsterdam and sit for lunch.