Burgers are not on the dinner menu, but if you ask they'll let you order one anyway. I don't recommend doing this though. I ordered a burger at dinner on one of our visits and the burger was not very good - it was tough and dry. Our family of four has ordered burgers at Sci Fi for lunch a total of 4 times, and every time they were delicious. I have also read posts by others that have had the same experience - they got the burger at dinner by requesting it, but it wasn't very good.
This is the reason I suggest having lunch at Sci Fi instead of dinner. It's such a fun place to eat, and the burgers and shakes are delicious at lunch, but I can't say the same for dinner.