Pour melted butter into a 9-in. square baking pan; sprinkle with nuts and brown sugar. Arrange pears over nuts.
In a large bowl, cream softened butter and sugar until light and fluffy. Beat in egg and molasses. Combine the flour, ginger, cinnamon, salt, baking powder and baking soda; add to creamed mixture alternately with water, beating well after each addition.
Spread batter over pears. Bake at 350° for 35-40 minutes or until a toothpick inserted near the center comes out clean. Cool for 10 minutes before inverting onto a serving plate. Serve warm with ice cream if desired.