Preheat oven to 350°.
Lightly spoon flour into dry measuring cups; level with a knife. Combine flour, sugar, and baking powder in a large bowl. Combine rind, 1 tablespoon lemon juice, extract, oil, and eggs, and add to flour mixture, stirring until well-blended (dough will be dry and crumbly). Turn dough out onto a lightly floured surface; knead lightly 7 to 8 times. Divide dough in half. Shape each portion into an 8-inch-long roll. Place rolls 6 inches apart on a baking sheet coated with cooking spray; flatten each roll to 1-inch thickness.
Bake at 350° for 30 minutes. Remove the rolls from baking sheet; cool for 10 minutes on a wire rack. Cut each roll diagonally into 15 (1/2-inch) slices. Place the slices, cut sides down, on baking sheet. Reduce oven temperature to 325°; bake for 10 minutes. Turn cookies over; bake an additional 10 minutes (the cookies will be slightly soft in center but will harden as they cool). Remove from baking sheet, and cool completely on wire rack.
Combine 1 tablespoon lemon juice and powdered sugar, and drizzle over the biscotti.