Prepare the filling. Combine the flour, sugar and ginger in a mixing bowl and mix well. Toss the sliced pears in dry ingredients until they are completely coated. Arrange the pears in the pie shell and pour any remaining dry ingredients into the pie shell.
Prepare the streusel topping. In a mixing bowl, mix together all the streusel ingredients except the butter. Add the butter into the mixture and mix together with two forks until pea-size crumbs form. Alternatively, add the streusel ingredients into the bowl of a food processor and pulse until pea-size crumbs form.
Top the pears evenly with the streusel topping.
Place pie onto a sheet pan and bake for 25-30 minutes or until crust and streusel are golden brown.