Oven shelf

transitionculture.org/.../

Note how the oven doesn't completely envelop the base as most ovens do.
With this arrangement, the smiling baker has created some shelf space for necessary supplies.

Brick Oven

www.chimkc.com/Worksamples/Bakeoven.htm

The oven above is not, strictly speaking, an earth oven, but the elements required to build it did come from the earth. If you have masonry skills, then you could construct a very classy oven like this one. I do like the stucco which makes an all brick oven less busy.
My skill level is fairly low, so I'll stick with the easy-to-build ovens.

How to Build an Igloo

www.monsterguide.net/how-to-build-an-igloo.shtml

Not exactly an earth oven, but you get the idea.

Stone Oven

www.earth-connection.com/plants.htm

Obviously not an efficient oven, but does everything have to be efficient? Looks like it was built with rocks from the neighborhood. If there's a thin, flat rock on the top, it's entirely possible to bake a flatbread on top of the oven while another bakes at the same time inside.

Bread Oven Manitoba Canada

www.mhs.mb.ca/.../13/selkirksettlement3.shtml
The Lord Selkirk Settlement at Red River, Part 3
by Anne Matheson Henderson

"Most of the homes had an outside oven in which bannock and later bread and pies were baked. These were used long after the modern stoves came into the settlement ..."
The oven is intact, but note how the square oven opening has sagged. A rounded opening would have been stronger.