Cheap folding solar cookerThis is not an original idea by me. Professor Steven E. Jones at BYU made the original here. I had problems with the design in three areas: Focal point, and lack of rigidity, and adjusting for the angle of the Sun.
Set up, but without the plastic bag, or reflecting funnel. The mason jar is held above the bottom of the funnel by a wood block on hardwood dowel. Coat hanger wire was used to make a cradle for the jar. The legs of the frame can be adjusted for the angle of the Sun.
Here it is ready for use. I have left out dimensions since your funnel would almost certainly be a different size.
Refer to the original site for notes on making the funnel, instruction for how to use, and recipes.