The impromptu Peruvian oven that is is built in the Peruvian highlands to bake potatoes can easily be adapted to bake bread. While the Peruvian watia dome is heated and then collapsed onto the potatoes, one can use the form to bake bread the usual way.
The Peruvian potato oven is constructed in situ with sod or weedy soil. If your soil has a high clay content then using clumps of soil that are already bound with roots is more or less equivalent to building a cob or adobe oven. I don’t know how big a dome one can build out of sod but if one doesn’t have a weedy field to dig up I imagine the following experiment: seed a prepared bed of clayey soil large enough to construct the dome of an oven that is three feet (1 meter) in diameter with grass and when the grass is well established shovel clumps to build an oven as illustrated below.
These videos are posted by the Standford University Clay Technologies Lab associated with the Department of Archeology.
The following video illustrates the loading of the watia oven with potatoes. The text that accompanies the video reads, “Ricardo, Lucho, Luis, and Genaro adding potatoes to the preheated earth ovens. First, they throw the potatoes through the door and onto the hot coals. Then, they open a hole in the top of the dome, collapsing some of the hot dirt clods onto the potatoes below, before adding the rest of the potatoes through the hole. Finally, they collapse the entire structure onto the layers of potatoes, break up the dirt clods and cover the mass with loose dirt. It takes 30-45 minutes to bake the potatoes. Footage by Melissa Chatfield (Clay Technology Lab) (July 2008)”