I use big flat mushrooms and remove the stalks. Make up some plain couscous with boiling water, mix in chopped spring onions, the chopped stalks, maybe some chopped tomato, but nothing too wet. Then I pile the couscous into the mushrooms, put grated parmesan on the top, and put it all into the oven until brown.
The couscous is crispy on top and moist underneath as it absorbs the moisture from the mushrooms.