I was never there at Christmas time but I had a really nice meal in an Irish restaurant called . Now, compared to Lanzarote prices, this was pricey but felt and tasted like a Michelin starred restaurant. We got 2 starters, 2 mail meals (fillet), one dessert, a glass of wine and a bottle of wine for about EUR90. The owner made us feel really welcome and the place was very busy.
They may be like a home from home on Christmas day. Would need to prebook I'd imagine.
There was another restaurant we went to where the food was really good (Magnolia) but its just a regular PdC restaurant. Dont think it would have the Christmassy atmosphere you'd be looking for