I have personally never done this, but I've been camping where an older friend of mine did just this thing with baked beans. (So good!)
From watching what he did, and I'm not sure if it's standard practice or not, he definitely at least started the cooking process over the fire. He got the dutch oven hot enough to get the bacon grease out and then added everything else in. I think the idea is to have this be the "high heat" part so the bacon wouldn't be "limp" (I apologize for not being able to think of a different word) and the onions could get a nice golden color. Then, he took it off the heat to shovel about half the ashes to the side. Covering it back up, he put it back on the remainder of the ashes and put the rest on top. At this point, he just let it be and didn't tend the heat/ashes anymore to keep it hot or anything, just letting it go. By the end of it all, with the ashes cool enough to brush off, this slow method made some great beans.
He told me you can bake biscuits and things in there, but I'm not sure how that works. I have heard you can best regulate the heat with dutch ovens using charcoal. I think this is because they hold heat better/longer than just ashes and burning wood. I even remember reading in a magazine that there is a "formula" to managing the heat. Just making this example up, but it might be along the lines of, "For 350 degrees, use 7 hot charcoals on the bottom and 3 on top." Each charcoal equaled a temperature change.
Now, that's just WAY too technical for me. Were it me, I'd leave it to things that you can basically heat for hours to cook slowly, like baked beans or stew. But, some people like a challenge!
Do you own a dutch oven? Have you done anything with it yet if you do? I think they're neat, but I have no experience with them.
This method is used in parts of Africa. Jollof rice is one of the most popular dishes in Africa and this is the traditional method for cooking it. I've cooked jollof rice using a Dutch oven a few times, it is delicious, but I've never underground. I would like to give it a try one day.