Roy
The basis design is simple and there are a number of ways to do it. I had intended on making one but finding one new so inexpensively was too good to pass up.
the difference between a solar oven and a solar cooker is that the oven is black inside to absorb the heat. A cooker reflects the light onto a black vessel that cooks the food inside. I took the oven out for a second test at 3 pm and after a half hour it was holding 225 without the reflectors. I didn't remove the lid when I brought it in and a half hour later it is still 125F inside.
The difference between the magnifying glass concept and the dish is the dish focuses the light from below like a stove would.
Here is a page of plans for solar cookers. I used a wash basin and black pot to heat water in the tenting days, it was nice washing up or doing dishes with hot water.
plans