Preheat the oven to 175°C. Spread the walnuts on a baking sheet and toast for 10 minutes. Increase the oven to 200°C.
Place the frozen pastries on a baking sheet lined with parchment paper. Bake until puffed, 20 to 25 minutes. Meanwhile, in a bowl, add the strawberries, balsamic and maple syrup. Mix. While the pastries are still hot, stuff with the cheese, and then top with walnuts, strawberries and some pepper. Serve hot.