There are two types of oven cleaner, spray-on lye and spray-on ammonia (well, triethanolamine, which is just substituted ammonia). These are strong bases that will saponify (turn into soap) all of the baked on grease and fat that has evaporated and deposited onto the oven walls. These aren't really environmentally unfriendly, you can dump the oven rinse water into the septic tank or the compost pile and other than a temporary pH rise, there won't be any long lasting problems and the microbes will eat it up.
The only way to do it without chemicals and major work is to have a self-cleaning oven, one that has an 'incinerate' setting which gets the oven up to 600 or 700 degrees and carbonizes all the baked on grease and fat. Then all you have to do is wipe up the residual ash with a wet paper towel. If it is not a self-cleaning oven, you might be able to do it by hand with a blowtorch, but that would take a little skill -- too hot and you damage the oven wall, not hot enough and you don't get it clean.
I'm afraid anything besides the self-cleaning setting is going to be labor intensive 
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