While I don't normally cook on the trail, a lot of people have been looking for lightweight grilling options for backpacking. At the supermarket today, I stumbled on to the Oscarware Grill Topper and thought some people might find it interesting.
The one I got was $1.50, measures 7" X 11" and weighs 0.8 oz. This one looks like a good size for grilling trout or for a solo hiker but they make larger ones and different shapes. It's little more than an aluminum mesh that you would have to prop up with rocks but looks like it would work pretty well. Now all you need is an ultralight spatula.