I have found most food truck to be waaaay over priced and often the food quality is severely lacking. That being said there is one truck I really,really like (outside some truly outstanding late night taco trucks). Try the Pokey truck
The Pokey Truck Japanese *Hawaiian**Wrap * - Home . They usually can be found around the Warner Bros. lot in Burbank at lunch time. They have terrific, huge burrito like rolls stuffed with crab, spicy tuna, and for the more adventurous out there, a very tasty eel! All rapped up in soy paper. Yum!
Usually, if you find one truck there will be at least two others right next to it. they will often times have links to websites or Twitter feeds that let you know where they are.
Good luck with your quest!
-Michael