We were in Lanzarote for Christmas day a couple of years ago. Our apartments actually had a snack bar and they put on a Christmas dinner for us all. However, there were lots of places open that you could book a dinner at. People were walking around decked in their Christmas hats etc on the beach.

Hopefully someone who has booked in one of the restaurants will be able to give you some recommendations.

The Lanis chain of restaurants can be recommended. Be aware that some places close early on Christmas eve as this is a Family get together time.