Get a low-medium fire going. You can cook this on a charcoal grill, a BBQ, or on a grill plate over a campfire, but aim LOW. It’s better to have a low fire and need to cook it longer, than to run too hot and burn it before it cooks! Spray your Dutch oven with nonstick spray, then line it with parchment paper, set aside.
In a large bowl, mash together bananas , oil, egg, and vanilla until relatively smooth.
Add a bag of Banana Bread Mix to the bowl. Use a wooden spoon or rubber spatula to stir just until combined, with no obvious streaks of flour in the batter.
Pour batter into your prepared Dutch oven, cover, and place over the grill.
Cook for about 10 minutes (15 if your fire is really low), then remove from heat.
Note: The cooking time will vary wildly based on your heat source and pan. Keep an eye on the banana bread - as it’s getting close to the point of needing to be taken off the fire, there will be a lot of condensation forming on the lid, the outer edge of the crust will start to get golden brown, and the colour of the batter will intensify. You want to take it off the heat when the bread is mostly yellowish and the outer edge is golden - any further will char the crust. WITHOUT removing the foil or lid, allow the banana bread to continue cooking in the pan for another 5 minutes. (This lets it cook through, without burning!).
Uncover the banana bread, and check to see if it’s done. When finished, it’ll be between 190-200 F when an instant read thermometer is inserted into the center of it. Alternately, a toothpick or bitter knife inserted into the center will be “clean” when pulled out. If it’s not quite done, return to the heat for another few minutes, the allow to sit for another 5 - without removing the lid. For best results, be sure to not overcook it, or it will be dry!
Allow the banana bread to cool slightly, before slicing and serving.