Prepare bottom crust by mixing together flour, margarine and pecans until crumblike. Press mixture into greased 13x9" baking pan. Bake at 350~F for 15 to 20 minutes until lightly golden. Cool. Beat cream cheese with sugar until smooth. Fold in half of Cool Whip. Spread mixture over cooled crust. Combine vanilla and chocolate pudding mixes. Beat in milk until smooth and thickened. Spread over cream cheese layer. Spread remaining Cool Whip over top. Sprinkle with grated chocolate. Cover and refrigerate overnight.