Gibson's Rosemont was my go to nice office lunch place for about six years when I worked in Rosemont. A couple of notables on the non-steak lunch menu:
The crab cake is a huge portion (one cake on the lunch menu was always plenty for me). It is somewhere around 99% pure crab served with a spicy remoulade. It was a long time favorite in my book.
The seared tuna salad is a generous serving of seared tuna served over a bed of salad greens with pistachios and a gingery Asian style dressing.
The appetizer crab meat and avocado salad makes for a filling lunch. Its about six ounces of snow white crab served with capers, roasted red peppers, a pepperocini with a thai style dressing over a fresh peeled avocado.
Usually, there is one lunch portion fish special on the menu- usually some sort of a tilapia with sauces or salsas made in the kitchen which can range from traditional (butter lemon) to downright wacky (raspberry mango salsa)
All of their steaks are available at lunch though it seems to me that sometimes the results of those items are not as good as they are at night. If you're there on a day in which lobster or shrimp bisque is the soup of the day, a cup of that is highly recommended.