In a medium bowl, whisk together flour, salt, baking powder, baking soda, cinnamon, nutmeg, and ginger. Set aside.
In a large bowl, beat sugar, brown sugar, egg, and oil.
Add dry ingredients.
Mix until just incorporated.
Add buttermilk and vanilla.
Mix in pears and walnuts.
Pour into prepared pan.
Top with streusel.
Bake for 50 minutes, or until done, covering the last 20 minutes or so.