Preheat oven to 350°.
Combine pears, 1 tablespoon ginger, and lemon juice. Coat a 9 x 2-inch round cake pan with cooking spray; sprinkle with granulated sugar. Arrange pears in bottom of pan in a circular pattern.
Combine brown sugar and butter in a large bowl; beat at medium speed of a mixer until well-blended. Beat in egg. Add buttermilk, molasses, and 1 tablespoon ginger; beat until well-blended. Lightly spoon flour into a dry measuring cup; level with a knife. Combine flour and next 6 ingredients (flour through nutmeg). Add flour mixture to batter; stir until well-blended. Pour over pears. Bake at 350° for 40 minutes or until cake springs back when touched lightly in center. Cool in pan 20 minutes on a wire rack. Place a plate sprinkled with powdered sugar upside down on top of cake pan; invert cake onto plate.