Preheat oven to 350. Line 9 x 13 pan with foil and spray with non stick cooking spray. set aside.
In large bowl, with electric mixer, beat margarine and 1/2 c. sugar til light and fluffy, about 3 minutes. Beat in 2 cups flour until fine crumbs form. Press into prepared pan. Bake uncovered for 20 minutes
Meanwhile, in medium bowl, with electric mixer, beat eggs, remaining 2 c. sugar, 1/3 c. flour, lemon juice and peel, 4 minutes or til light and fluffy. Pour over hot crust.
Bake an additional 25 minutes or until lemon mixture is just set. Cool completely on wire rack. Using foil, lift out of pan. Spray knife with cooking spray and cut into triangles.
to serve, sprinkle with confectioners sugar, to your liking.