I spent a couple of days in D.C. last august. The first time was so good that we decided to go there the day after too. You can choose which kind of base you wish. We always choosed salad. Then you can mix whatever you want: veggies, meat and so on. Finally, you choose the dressing (holy s'hug!) and the sides: amazing falafels and hummus, with a hot pita.
Kevin is great and if is the first time you go there he tells you everything you need to know. I don't know when I'll be back in D.C., but I'll definitely go there again!