When I was off grid I used a solar oven. Mine was made of four 15" (38cm) shiny reflective thin pieces. The pieces feel like thin plastic placemats (NOT the squishy ones) with the shine on just one side. To mimic mine you could make similar using the dull side of heavy duty aluminum foil.

Cut slits one inch from each corner along what will be you bottom side. You will insert the pieces together at the notches/slits to form a square (or rectangle if you use a placemats as is). Have the shiny side inward.

The key in my opinion is the pan you use for baking. For that, you will need a black pan with a lid. I found a small black enamel pan with a black lid at a thrift store.

Add one chicken in the pan. Season as desired. Garlic pepper is my preference. Put the lid on your pan. The black pan-with-lid combo will cook your food on a sunny day in a few hours.

Do NOT open until it smells like chicken. When you open the lid the heat is released from the pan, this lengthening cooking time. It will smell amazing when fully cooked even with the lid closed. Yes the color will be normal for cooked chicken.

Frankly I know the theory on the reflective properties of the shiny aluminum cooker focusing the sunlight on the pan. Because mine was so easy to utilize I did so however a black pan set in full sun should work nearly the same. I suspect we overcomplicate our lives with stuff.

I only used mine to cook chicken. It worked well. Good luck.