In the past, for lunch service they would replace the low tables with long cafeteria-style ones, much more conducive to eating rather than the low, modular furniture for the night time lounging and drinking activities. You would order at the bar, take a number, and your meal would be delivered soon afterward.
I stopped in last Friday for the first time in about 6-8 weeks and they've reverted back to the lounge furniture for lunch which I find rather irritating, so I opted to sit at the bar. They've added table service as well, and they were much busier than I have seen in the past. Staff continues to be wonderful.
Personally, I think the lunch service at Middlesex is one of the most slept-on deals in the MIT/Central area. Wonderful salads and you can add a 1/2 pressed sandwich for a few dollars more. My favorite is a salad of romaine with shredded roasted chicken, gorgonzola, cherry tomatoes and cilantro with a nice light vinagrette. The turkey sandwich is always good, and on my most recent visit I tried the roast beef - pressed with cheddar (IIRC) a sweet tomato-pepper chutney with a side of mustard dipping sauce. Picked carrots on the plate are a nice added touch.