Preheat the oven to 375 degrees F (190 degrees C). Grease a 2 quart casserole dish or 9 inch square baking dish.
In a medium bowl, stir together the oats, brown sugar, 1/2 cup flour, 1 teaspoon crystallized ginger, and cinnamon. Stir in the butter until the mixture is crumbly with pea sized lumps. Set aside.
In a separate bowl, stir together the white sugar, 2 tablespoons flour and 2 teaspoons of crystallized ginger. Add the sliced pears, and toss to blend. Transfer to the prepared baking dish. Spread with the oat topping.
Bake for 30 to 35 minutes in the preheated oven, until pears are soft and topping is golden brown. Cool slightly before serving with vanilla ice cream.