After a lot of trial and error and redesign I managed to make this fairly portable and storable fresnel lens and mirror arrangement. The starting point was my normal fresnel lens solar cooker. And it works, as you can see by the fried egg below. It took around 5 minutes for the cast iron pan to warm up enough to sizzle droplets of water and then around 2 minutes to cook the egg and 20 seconds to eat the egg sandwich (yum!).
The mirror is an ordinary mirror that someone thew out years ago and that I cut to the length I figured I'd need. On the right below I flipped the mirror on its back so you can see that the mirror is not at the focal point. It's only part way and that's why the mirror doesn't get hot enough to crack from temperature gradients.
The very cool thing about this is that you can look down into the mirror and see the sunlight on the bottom of the pan. In the photo on the left below you can see that the pan is also not at the focal point. Instead it's placed such that the light coming from the mirror is spread out over the whole pan bottom for even heating. In the other two photos I swivel the pan off center so you can see the edge of the light coming from the mirror.
The heat from the sunlight coming from the bottom of the pan isn't as fast at cooking as the sunlight coming directly from the lens. The nice thing, as the following photos show, is that if you want some of that faster cooking heat you can just push the pan forward more over the mirror and intercept some of the sunlight going from the lens to the mirror.
And here's a video showing it's assembly and use. Enjoy!