Place water in a medium saucepan. Add ½ cup sugar and bring to a boil over medium-high heat. Add pears to the pan and cook for 10 minutes, covered. Drain and set aside.

Preheat the oven to 375°F. Lightly brush a 9-inch pie pan with vegetable oil and line it with the pie crust.

In a large bowl, whisk the eggs with butter and ½ cup sugar. Add the sifted oat flour and potato starch, cocoa powder, cinnamon, and vanilla. Whisk to combine. Pour the filling into the pie crust. Arrange pears on the filling. Bake for 40 minutes or until filling is set.

Remove from the oven and top with melted chocolate. Allow the pie to cool for at least 30 minutes before serving.