Lunch near Dulles
Will you have a car? Where are you from? What do you enjoy?
To give a few things after that interrogation, there are a few good places at Reston Town Center, notably Jackson's, Mon Ami Gabi and Passionfish (I listed those in reverse order of my personal recommendation, btw).
There's good German at Euro Bistro in Herndon. Good Mediterranean at El Manantial in Reston. Great escargots and martinis in an al fresco setting if the weather is nice at Cafe Montmartre at historical Lake Anne, Reston (come see what the crazy hippies built in the early 70's).
Two great kabob places are in the area, some solid Thai, Jamaican, Ethiopian, and more.
327 7th St SE, Washington, DC 20003
Mon Ami Gabi
7239 Woodmont Avenue, Bethesda, MD 20814
If you're at an airport hotel and heading to the airport, you probably don't have a car. Ask the hotel where they have shuttle service to and from. Most likely the serve to Dulles Town Center, where there are plenty of restaurants, nothing really exotic but there are several real sit-down restaurants that are more interesting than a food court.
Don't miss your flight.
Though the Kabob place in the food court is surprisingly good. Easily the best food court offering I've ever witnessed.
And I'd bet they'd take you to Reston Town Center, which is closer.
In either case, I'd make sure about logistics of them picking you up again and getting you to the airport in time.