Heat oil in a medium nonstick skillet over medium heat. Add the mushrooms and onion. Cook, stirring frequently, until most of the mushroom juices have cooked out, about 4 minutes. Sprinkle with flour, stirring to mix well.
Stir in sherry, salt and pepper. Cook and stir until mixture is almost dry, about 2 minutes. Remove pan from heat and set aside to cool slightly.
Preheat oven to 400 minutes.
Have an ungreased baking sheet ready. Separate biscuits and place them between two sheets of waxed paper severl inches apart. With a rolling pin, roll biscuits into 4 to 5 inch circles. Carefully remove the top sheet of wax paper.
Using a heaping tablespoonful of filling, place slightly off-center on each circle. Carefully fold biscuits over, making a half-circle and stretching the dough gently over the filling. Crimp the edges together with a fork. Place pastries on baking sheet.
Bake 8 to 10 minutes, until golden brown. Serve hot or at room temperature.