You can do anything with charcoal.
One trick that we used to do when we were camping was to line a cardboard box with foil. Several metal grates or skewers would be stabbed into the box walls and a grate with a few coals hung near the bottom.
We would use it to bake bread and pizzas. To control the temperature use more or fewer coals.
As long as you are building things- another option to consider is solar oven.
They consist of an insulated container, a transparent window, and a reflector. There are a great many models to choose from. Some of the more permanent models can get above 350F as long as there is direct sunlight.
This model was just one of top results from Google but it is a typical design: