Heat oven to 375°F. Lightly spoon flour into measuring cup; level off. In large bowl, combine 1 2/3 cups flour and 1/2 cup powdered sugar; mix well.
Using pastry blender or fork, cut in margarine until mixture resembles coarse crumbs. Press mixture in bottom of ungreased 13x9-inch pan. Bake at 375°F. for 14 to 17 minutes or until edges are light golden brown.
Meanwhile, in medium bowl, combine all filling ingredients except lemon juice and lemon peel; blend well with wire whisk or fork. Stir in lemon juice and lemon peel. Pour filling over base. Bake an additional 18 to 25 minutes or until center is just set. Cool completely. Sprinkle with 2 tablespoons powdered sugar.