Combine pears and lemon juice in a large bowl; toss gently. Sprinkle with 1/2 cup sugar, 1/4 cup flour, and lemon rind; toss well. Arrange the pear mixture in the pastry shell. Set aside.
Combine 1 cup flour, brown sugar, cinnamon, and nutmeg in a medium bowl; stir well. Cut in the butter with a pastry blender until the mixture resembles coarse meal. Stir in the chopped pecans; sprinkle the pecan mixture evenly over the pear mixture.
Bake at 400 degrees for 25 to 30 minutes or until the pears are tender and the crust is a golden brown.