Anything with avocados or artichokes screams California to me.
For specific foods that come from California, I'm thinking carne asada fries or In-n-out Burgers (make your own copycat version.) But there are also large Hispanic and Asian populations so that means lots of Hispanic and Asian foods. Also there's a huge coast so that means lots of seafood, too. There's so much you can do with "California" food! Care to narrow it down a little, OP?
If you wanted to do more of a general theme, here are some:
-Orange County, CA. Make everything look like orange or taste like orange.
-Hollywood. Base the menu off of your movie of choice. For example, make your own pizzas while watching the award-winning film Mystic Pizza starring a young Julia Roberts.
-San Francisco. Eat a whole bunch of Rice-a-Roni.