The sandwich was previously a summertime offering exclusive to Subway locations along the Atlantic coast of the country and features chunks of lobster meat mixed with mayo with the standard choice of toppings and bread (although the recommendation is for a simple pairing of lettuce on toasted Italian bread).
It should be noted that while the Lobster Sandwich hasn't been offered here in the States, Quiznos regularly offers such around Lent as does McDonald's (with the McLobster in Maine).