Preheat oven to 350°.
Heat a large nonstick skillet over medium heat. Add first 6 ingredients; cook 5 minutes, stirring occasionally.
Place pear mixture in a 2-quart casserole lightly coated with cooking spray.
Lightly spoon flour into a dry measuring cup; level with a knife. Combine flour, 1/2 cup brown sugar, 1 1/2 teaspoons ginger, and salt; cut in butter with a pastry blender or 2 knives until mixture resembles coarse meal.
Place bread in a food processor; pulse 10 times or until crumbs measure 3/4 cup. Stir breadcrumbs and nuts into flour mixture.
Sprinkle flour mixture evenly over pear mixture. Bake at 350° for 40 minutes or until filling is bubbly and topping is golden.
The slight heat of ground ginger brings out the sweetness of the pears. Ground gingerroot is far more intense and peppery than fresh. If you prefer only a hint of ginger, omit it from the topping.