Restaurant Options During Layover

I would not recommend leaving the airport. It could easily take an hour to get through immigration, you need to be back in line for security at least 2 hours before your flight departs, and it will take an hour for transportation to and from London on the fast and very expensive Heathrow Express. If you take the tube it will be longer. In the best case, that leaves you one hour free. If your flight happens to depart out of Terminal 5, you might go have lunch at the Gordon Ramsay restaurant called "Plane Food".

I agree with Laura. I would be sweating bullets the whole time I was dining if I knew that there was any chance of missing my connecting flight.

Which airport are you flying into? I would assume Heathrow (I think most, if not all, Boston flights land there). If so, here's your likely time table:
IF your flight lands on time (not all the probable, but let's hope), you will deplane sometime between 1:00 and 1:30 (some flights park at 'remote' gates and you have to board a bus to get to the terminal). Immigration will take anywhere from 15 min. to 2 hours if you leave the terminal. At best you could catch the Heahtrow Express (fastest and most expensive transport to London) around 2:00. That puts you at Paddington Station around 2:15- 2:30. You need to check in for your flight around 3:30. That means leaving no later than 3:00. You might not even have an hour to find a restaurant, order and eat before you are rushing back to catch the train back to Heathrow. One glitch and you miss your next flight. Not a risk I'd want to take. There are plenty of restaurants in all of the terminals at Heathrow. Lots of shops, too. Or you could shower, rest and relax in one of the airline lounges (you can buy a day pass if you don't have the proper 'status'). Or get a room at the Yotel (the sell rooms by the hour) and have a bed to stretch out on for a nap. If you are flying into Gatwick, there is absolutely no way it would work as the journey into Victoria Station on the Gatwick Express takes just over 30 min.

All the advice above is what you should pay attention to. Here is what I would do. In my paranoia bag, otherwise known as the 3-1-1 bag I would have several 100ml/3.2oz. bottle of my favorite alcoholic berverage. I can get about six legal bottles in here. Then I have some sort of granola or energy bars, some Baker's semi-sweet chocolate squares, and some other candy, and some trail mix. I really don't know what more a person would need to kill a few hours in any airport.

Eat lunch at airport. Leave at your own peril.

@Monte, thanks for the chuckle!!!

Stay at LHR. Lots of places to grab a nosh. EAT. BITE. Pret a Manger. Wagamama.

Enjoy a nice sandwich in the airport at Pret a Manger, which still offers better choices than the sorry excuses for Pret a Manger that are now here in Washington and New York.
You have a comfortable layover time, but not a long one that would suggest leaving the terminal.

Last summer, we had a 9 hour layover at Heathrow. I thought , "Let's go the British Museum - it's free!" For 4 of us, the Heathrow Express was L 16 each, or L 64. That is, about $120 for the train in and out of town. Still, the museum was free.