As you walk on the dock just after you get off the boat toward the GF, just as you step onto land at the end of the dock Narcoossee's should be at your left. There's a door that you can see from the dock area, this is NOT the main entrance. Keep walking toward GF maybe 10-20 yards , turn left onto the walkway and you'll run into the entrance, there's a sign but it's not the most visible thing ever... I think it's either in red or orange.
The whole restaurant kind of looks like huge gazebo thing.