Preheat the oven to 425 degrees F. Spread the unbaked pie crust into a 9-inch pie pan and crimp the edges.
Add the sliced pears to a medium bowl. Drizzle the lemon juice over the sliced pears. Set aside.
In a small bowl, combine the sugar, flour and nutmeg. Sprinkle over the pears to coat. Pour the pears into the unbaked pie crust.
PREPARE THE TOPPING:
In a medium bowl, use an electric mixer to combine the topping ingredients. Spread over the pear mixture.
Insert the pie pan into a brown paper bag. Fold the edge and fasten securely with staples to create a sealed environment. It's helpful to take a rack out of the oven so you can put the pie on a lower rack. As long as the bag isn't touching the heat element, it won't catch on fire. Place on a cookie sheet and bake for 1 hour.