Was in Chelmsford today for a work meeting and stopped into the Chelmsford Centre Deli. I highly recommend this spot. Old-school service, toughie workers, and a drippy oily Italian sub laden with hots. Great hot specials too. It is in a bland plaza near the Marshall's.
If in the area may I also recommend the Lowell Portuguese Bakery on Gorham Street. Area is a bit shabby, but you won't find a finer, more authentic bakery. It is just off the Connector.