Within 6-9 blocks there are so many great places. I would strongly encourage you to go to Breadline on Fri. when they have pulled pork - ask for it on ciabatta. This is one of the best sandwiches in the city. G Street Food for a good bahn mi sandwich and plenty of other choices. Teasim - get the salty oat cookie for dessert. Cowgirl Creamery for wonderful prepared sandwiches. Taylor Gourmet for Philly-style subs, and the Juice Joint for good and healthy fare.
Soon you will have a Pret a Manger: http://chowhound.chow.com/topics/686982
It's worth the walk to G Street Foods and Breadline. And soon to be opened next door, roti
You could consider walking to Taylor Gourmet in Mount Vernon Square. Not sure if that's too far...
Doesn't Zengo have some sort of lunch bento box special?
1116 H St NE, Washington, DC 20002
781 7th St NW, Washington, DC 20001
G Street Food
1706 G St NW, Washington, DC 20006
There is a good deal at the bar at Proof for an entree and glass of wine for around $13. Also Zola Wine Kitchen also normally has like $11 lunches.
I also like Matchbox and Zaytinya (some of the lunch items are very reasonable). There is also Cowgirl Creamery for prepared sandwiches, Nando's Peri Peri. For a longer walk there is Potato Valley. Right near you is Cafe Mozart, Bredline and G street, Ella's woodfired Pizza, Potenza and you probably aren't too far from Teaism. And there is always Ollie's Trollie (sp?).
2009 R St NW, Washington, DC 20009
701 9th St NW, Washington, DC 20001
1331 H St NW Ste A, Washington, DC 20005
Potato Valley Cafe
614 E St NW, Washington, DC 20004
1430 H Street, NW, Washington, DC 20005