Get a campfire going and let it burn down for about 10 minutes, or until you have some coals in the fire.
In the dutch oven layer chips, cheese, beans, and olives: Spread a layer of chips on the bottom of the cast iron. Top with 1/3 of the shredded cheese and a couple of spoonfuls of the drained beans and olives (if using). Repeat this layering at least 2 more times. If using a 4 Qt. cast iron, you can fit about 3 layers.
Put the lid on the dutch oven and place it near (but not on) the fire. Carefully put 1-2 coals under the dutch oven, and 4-5 coals on the lid. See the video for a demonstration.
After 10 minutes, carefully use a fire glove or lid lifter to check on the nachos. The cheese should be melted. If not, add fresh coals to the lid and wait a few more minutes before checking again.
Once the cheese has melted, remove the dutch oven from the fire pit and carefully add your toppings. Serve immediately.
Notes
If you notice that one side of the dutch oven is hotter than another, simply rotate the dutch oven 180° to even things out.