Colesville Rd. near Fenton St., Silver Spring
7/10 on my bangin' scale
Located approximately diagonal ("catty-corner") from the Fillmore, I'd say Pho Tan Vinh is a pretty good option to fill your stomach for cheap before heading to a concert. The best bet if you're looking for a lighter meal is the grilled chicken banh mi:
At $5 and change, the chicken banh mi has the deliciously concocted crispy bread, cilantro, cucumber, carrots, mayo, and jalapeno that I've grown to expect, along with a tasty surprise--pate. For a more filling plate, consider trying the Tan Vinh special, which is a deconstructed banh mi with four different meat toppings (pate, sausage, egg, and some type of bologna). These specials are a little confusing at first--how can you fit all the toppings onto the crusty roll? You have a few options: 1) fork and knife it all the way; 2) make a REALLY full sandwich (not actually possible to fit everything on there); or 3) slice up your bread and make several open-faced sandwiches. This is the way to go if you want to make your own ultimate banh mi (or if you're just pretty hungry).
I've been missing the plethora of Vietnamese options in Seattle. So far, Pho Tan Vinh is the place I go to fill that lonely spot in my stomach.