The super-focus of a Fresnel lens allows the temperature of the device to be easily controlled, and with it's various attachments can be used as a solar oven, stove, BBQ, food dehydrator, water heater/distiller, and even a rotisserie.
The thin, light & super-efficient Fresnel lens, originally used to distribute light in lighthouses, directs the sun onto a mirror inside the cooker's main frame, and is then directed to the chamber on the left where the cooking, heating, BBQing, etc. is done; the mini-solar panels on the right power the auto-tracker, ensuring that the solar chef never need adjust the cooker until the food or water is ready. It can even be used indoors!
Here's a video that shows how it works:
Pretty cool if you ask me!
Check out California Sunlight's website for more information.