When my daughter was in college in Boston a few years ago, we enjoyed PHO PASTEUR downtown in the "theater" district at 682 Washington St. Very fresh & simple Vietnamese food, and inexpensive. Not much ambiance, though. I think they have a few other locations around the city.It is a few blocks from the Common.
We also took many folks to dinner at MAGGIANO’S (also downtown, at 4 Columbus Avenue). It’s a big, bustling friendly place with pretty good red-sauce Italian food & large portions. Medium-range prices, and nice people. OK- I know, it’s a chain, but you asked.
There are many good (or better restaurants in Boston. If you are not familiar with the city, my best suggestion is: ditch the car ann walk. Boston is agreat walking city, and a very bad driving city. many downtown streets are still better suited to horses and carriages.
If the weather turns nice in 2 weeks, you will have a wonderful time.