Welcome to the Dis.. I believe it is the lunch menu for lunch and dinner for dinner, but it never hurts to ask the server if you can have something you saw on the dinner menu if you are there for lunch and vice versa. All they can say is no....but maybe they will say yes.
Depends on where you go. At Le Cellier DH was able to get the BBQ filet for lunch but I could not get the mushroom filet because they did not have the items prepped yet