This helpful hint came from the cheaprvliving.com forums

How to make a stove-top oven

From the Peace Corps Cookbook (2004):

If you don’t have an oven that does not mean you cannot bake. With these directions you can make a little stove top oven. Sometimes they are called a Marmite oven. There are many different options, so find the one that best suits you. Anything that needs baking can be done in a Dutch oven. It will take some experimentation but is certainly fun. Be Creative!
GUINEA DUTCH OVEN
What you will need:
1. A large pot with lid to serve as the oven (even a large tin can will work if you have one  like those big NIDO dry milk cans, or popcorn tins)
2. A smaller pot or bowl to fit inside and serve as the baking pan (this must fit inside the bigger pot with the cover closed. Metal graniteware bowls or mini glass bowls work well; no plastic handles though as they will melt.)
3. Sand, small rocks, or empty tomato paste cans (3) to raise the inner pot or bowl off the bottom of the big one. This allows the heat to flow around the inner area.
4. A stove or fire with consistent heat

Place the sand, rocks, or cans inside the larger pot. Place on the fire to ‘preheat’ the oven. After about 5 minutes, place what you are baking (in the smaller pot of course) into the makeshift oven, and close the lid. Voila! You are baking. Check the goodies often, as the temperature is hard to regulate, and things bake much faster than in a ‘regular’ oven. Rule of thumb for cakes and quiches is to stick a fork in the middle. If it comes out clean, and the edges pull away from the edge of the inner pan, it’s done.

You can also make a ‘wet marmite’ oven by putting enough water in to come up the tomato paste cans about 3/4 of the way up. Put your bake pan on top of the cans, but cover tightly with foil. Put the lid on the big can and bake away. The water helps keep the bottom of the large pan from getting hotter than the sides and burning out or breaking. Use this over a high flame to cook faster. Good for lasagna, banana bread and roasts that tend to get dry. The steam keeps them moist.

Clean sand on the bottom of the oven is best for things that require dry heat to bake, like bread or pizza.

If you use aluminum cans as mini-pans, you need to bake them once in the oven to burn off any paint, plastic linings, etc. Bake over high heat about 40 min. If it stinks, it is working.
Tin cans as pots:
1. used small tomato paste cans make good muffin and cupcake tins
2. sardine and tuna cans make good small cake, bread, and pie pans
3. small pots that fit in the large oven (lids are helpful) are good for larger loaves of bread and small roasts
4. For pizza, purchase a pizza pan that will fit inside a sand filled version, or cut down a coffee-can to make a cake type pan. Be sure to work the cut edges with some concrete to file off the finger-cutting edges a bit. I find a used, round aluminum cake pan (from the thrift shop for 50 cents) works to hold a one-person size deep dish pizza. For store bought thin crusts versions, turn the cake pan over to act as a cookie sheet and lay it on top.