I snapped this photo on Wednesday after riding the train with my son (highly recommend activity.
Here is more from the Hermann Park Conservancy page:
Great news! Becks Prime will be operating the cafe at Hermann Park during weekends in March and the week of Spring Break (March 5, 6, 12-20, 26, and 27). They will open for lunch each day at 11:00am. The cafe is located in Lake Plaza (adjacent to the main Houston Zoo entrance) between Kinder Station and the pedal boat lagoon.
So it sounds like it is a limited time only. If you have kids, don't worry, the site says there is a child's menu available.