If you want a late lunch in the Loop area, you pretty much are out of luck, other than fast food or pubs. The real restaurants shut down at 2pm and reopen at 4 or 5pm. If you like pubs, you have many choices, but that kind of food is too heavy for lunch on a hot day.
Cactus Bar and Grill, just south of the loop, offers an alternative. The fare is lighter, not the Tex-Mex you would expect based on its name. I had a special with sushi-quality tuna seared and placed on top of an excellent salad. Their house dressing on the side was very good. The music can be loud, but it was good stuff. Again, not Tex-Mex, but the classics. You know, things like Jumpin Jack Flash. There’s outdoor seating, but imagine this: it was too windy that day.