I've just spent a few days in Essaouria and i was pleasantly surprised. It was a lovely place, very laid back but after spending a few weeks in the countryside the level of harassment took a bit to get used to!
I have 2 restaurant recommendations that I thought I would share as I also ate lots of awful food while I was there!
The first is one called Il Mare which is a seafood restaurant overlooking the fort, sorry I don't have the address but it's down the end of an alley! There were about 10 of us eating there and not one of us was disappointed. It is a little pricey compared to Moroccan prices but well worth it for something different.
The other is a tiny little restaurant called Le Decouverte, it's run by a French couple who also do eco-tourism tours around the area. They were both really lovely and the menu was small but full of variety and it also has a specials menu that changes daily. The address is 8 Bis, rue Houmman, El Fatouaki.
Hope this helps someone!