One of the most universally useful cooking techniques I've found is "fireless" cooking. Technically, this isn't completely fireless, but it's a method that vastly reduces the amount of fuel needed to cook many foods, especially those like beans which take a long time. You can see a video of me explaining the process to some pastors here (you don't even have to download the video this time!).
I've shared about this before (scroll way down to the bottom of the post), but I had an opportunity to practice it with some of the staff of one of World Renew's partner organizations here in Uganda.
Not only does a fireless cooker save fuel (therefore saving money and caring for God's creation by not needing to cut so many trees for firewood or charcoal), but it also can help with health - not having to stand over a smoky fire for hours watching food cook, and it saves time - you can go do other work while the food is cooking instead of needing to be constantly keeping an eye on it.
We soaked beans overnight, then boiled them for 10 minutes.
Then we covered the pot, wrapped it in a towel, packed it into the fireless cooker and covered it with more blankets.
After 4 hours, it was the moment of truth:
Are the beans really fully cooked?
They were! Fully cooked beans, only using about 20 minutes worth of fuel (to bring them to a boil then boil for the 10 minutes).
As I've been sharing more about fireless cookers, I've learned more about them. They were basically the original crock pot and the rule of thumb is to put your food into the fireless cooker for twice the amount of time it would take to cook it normally. I need to do some more experimenting myself on other types of food besides beans, beans + maize, dried sweet potatoes, fresh sweet potatoes, and rice (the things I have tried before). But the staff who tried this with me were excited to go home and try it themselves, as well as to teach it to the rural communities where they work.