How can I warm up/cook food while cycling? I've been doing lots of long-distance cycling this year (150+ kilometers). With that much riding, there's obviously a need for some sustenance, and I'd rather not stop just to eat. 

The protein/carb bars have been getting incredibly boring... especially for my second meal on the road, so I've been experimenting with different foods like sandwiches and soups in a thermos. That's worked just fine, but it got me thinking... is there any system that I could use to cook or heat-up food while I cycle? 

It's crazy, I know, but when I was a kid, my father would cook food on the engine block while we drove... and I was thinking, that's almost a reason to start driving again :). Any thoughts on what I could do to heat-while-I-ride? Chemical heat? Electrical? Propane?

The latter (propane) seems dangerous and not so environmental friendly, but I suppose it couldn't be that bad?
I don't think it would be convenient or practical to use any kind of stove or hotplate while you are actually riding. If you are carrying a backpack or have things on a rack a propane backpacking stove can be very fast for creating a hot meal on a break.

To cook/warm while you are actually riding I think your best bet would be to use a Flameless Ration Heater like you find included in many military-style Meals Ready to Eat (MREs). I think you would still want to assemble the FRH and MRE into a packet and attach them to a rack while you ride because the packaging can get pretty warm.