On a recent trip to DC I tried out District Taco. This small chain offers fresh tacos and burritos that are made to order. Unlike Chipotle, this fast food Mexican restaurant has you select your ingredients and pick your protein from a menu. The cashier takes your order and the kitchen delivers your meal (or calls your name). Pretty conventional.
I tried a chicken and a carne asada taco. Both were tasty and flavorful. The side of cheese sauce that was optional was for the chips. There is also a nice salsa bar with a number of different choices.
Since you are building your own tacos here you really cannot complain about what they give you. The flavor of all the ingredients was great. Fresh tasting, not processed. The meals were appropriately-sized. Not generous, but not skimpy either.
They serve Boylan brand soft drinks. These "natural" sodas have real sugar and come in a variety of flavors including a standard cola. Nice touch and an easy way to set District Taco apart.
When in the DC area, check out District Taco.