One of the best places around BU campus to eat has to be Audubon Circle. It has a simple, modern decor, with some tables lining the black walls and a very sleek (and long) black bar. Check out an older visit here. They a variety of simple dishes, and put out very reliable pressed sandwiches and burgers. They also do a good job with ribeye. On weekends it gets a bit busier as the bar crowd fills up. It's a great spot to stop for a nice lunch though. 
crispy cod cakes, roasted corn tartar - $8 
burger with swiss cheese, onions, portabello mushroom, and roasted potatoes - $8 I think the prices may have gone up by a dollar or so, but it remains an extremely good deal. The cod cakes came out hot and crisp, but were a bit dry on the inside. I guess when I saw it listed I was reminded of the bacalao I had at Piperade back home. I set the bar high, but I wouldn't order these again... probably the worst thing I've tried on the menu. The burger, on the other hand, is pretty damn good. They're not afraid to cook it medium rare and it comes out very juicy. The bun and the toppings are all exceptional. It's not Mo's, but it's the best burger I've had near campus (far better than the one I had at Sunset Grill). The roasted potatoes are very well done, but honestly I still prefer fries with my burgers.