Preheat oven to 200ºC . Peel pears and cut into bite-size pieces. Set aside. In a large bowl, combine remaining filling ingredients and fold in pears. Pour pear mixture into pie crust and bake at 200ºC for 15 minutes Lower heat to 180ºC and continue baking for 25 minutes more. Mix together topping ingredients. Remove pie from oven and sprinkle topping over filling. Raise heat to 190ºC and bake until topping is brown.