Any tips on how to keep plants cool during the hot summer months?

[JDPriestly]

I'm in Southern California. My lettuce is going to seed as is my arugula. Cilantro will be impossible in the summer. I'm giving up on these vegetables much as I love having them fresh. My last hope is that someone on DU can suggest a way to keep plants really cool during our very hot, very sunny, dry weather. Any suggestions? I know about mulching with plastic. But that probably isn't really enough.