Zanzibar's most photogenic restaurant is perched on a coral outcrop in a stunning location surrounded by sea. At low tide you can walk to it; at other times (maybe after a long lunch) boats are provided. Of course, you're paying for the location, but the food is good and unsurprisingly includes prawns, lobster, crab, fish and other seafood.
The Rock is just off Kijiweni beach, opposite Upendo (villas and restaurant) about halfway between Michamvi and Bwejuu. Reservations recommended.