Preheat oven to 375. Line pie tin with crust. Sprinkle cake crumb into pie crust.
In small bowl, combine sugar, cornstarch, ginger root, cinnamon, and nutmeg. Mix well; set aside.
In a large bowl, combine blueberries, juice, and zest (go light on zest). Mix gently and fold into sugar mixture. Pour into shell. Set pan on baking sheet. Bake at 375 for 15 minutes.
While pie is baking, combine first five topping ingredients. Cut in butter until mixture resembles small peas. After pie has baked 15 minutes, sprinkle topping on hot pie. Reduce oven to 350 and continue baking for 60 minutes. If topping over browns, cover loosely. Cool 6 to 8 hours.