Preheat oven to 350°F. Melt butter in heavy 10-inch-diameter ovenproof skillet over low heat. Remove from heat. Sprinkle with brown sugar. Arrange quartered pears in flower design atop sugar, cutting some pieces to fit center if necessary.
Whisk flour, 2/3 cup sugar, crystallized ginger, cinnamon, baking soda, ground ginger and salt in medium bowl to blend. Whisk eggs, oil, vanilla and orange peel in large bowl to blend. Mix in grated pears. Mix dry ingredients into egg mixture.
Carefully pour batter over pears in skillet. Bake cake until tester inserted into center comes out clean, about 40 minutes. Cool cake in skillet on rack 20 minutes. Run knife around skillet sides to loosen. Place plate on skillet over cake. Invert cake onto plate. Serve warm.