Preheat the oven to 220C/425F/Gas 7.
Heat the oil in a frying pan over a high heat. Add the sage and breadcrumbs to the pan and cook for two minutes, stirring, until toasted.
Remove the frying pan from the heat and add the Brie, stirring to melt and combine.
Place the mushrooms on a baking sheet and stuff with the Brie mixture.
Place the baking sheet into the oven and bake for ten minutes, or until melted and golden.
Meanwhile, for the salad, place the ingredients into a bowl and mix together.
To serve, place the salad onto a plate and place the mushrooms on top of the salad.