Oh, a note on the walker thingies, you don't need spirit form to get past them, you can eat them too.
EDIT: Where the heck do you get the third cooking slot and what is this "Simon Sez" monster boss thing?
In order to get the third cooking slot you have to beat the "Simon sez" monster's challenge.
First, go to the Arnassi ruins which is divided into two maps: The first map is the racing circuit, the second map is the darker one with the giant crab boss and the secret ancient turtle. Search the lower left walls (western part of the cave) for a hidden passage (use the sun form) which you can only see on the minimap. When found (should be hidden near a giant arnassi statue), switch to Fish form and you'll find the ancient turtle. Ride it into the Kelp Forest, swim left and rightclick the boss to start the challenge.
He will roar if you fail the challenge, but won't do you any harm.
