Preheat oven to 375°.
Combine first 6 ingredients in a large bowl, tossing well to coat. Spoon mixture into an 11 x 7-inch baking dish coated with cooking spray.
Lightly spoon flour into a dry measuring cup, and level with a knife. Place flour, cinnamon, salt, and mace, if desired, in a food processor; pulse 5 times or until well combined. Add butter, and pulse 20 times or until mixture resembles coarse crumbs. Add the oats and sugar; pulse 5 times or until well combined.
Sprinkle oat mixture over pear mixture. Bake at 375° for 1 hour or until topping is golden and filling is bubbly. Cool on a wire rack 10 minutes. Serve warm or at room temperature.