Preheat oven to 350°F.
Line 8-inch square baking pan with foil, with ends of foil extending over sides of pan; set aside.
Combine crumbs, ½ cup flour and the brown sugar in medium bowl.
Cut in margarine with pastry blender or two knives until mixture resembles coarse crumbs; press firmly onto bottom of prepared pan.
Bake 15 minutes.
Meanwhile, beat cream cheese spread and granulated sugar with electric mixer on medium speed until well blended.
Add eggs and 2 tbsp flour; mix well.
Blend in 1 tbsp of the lemon peel, lemon juice and baking powder; pour over crust.
Bake 25 to 28 minutes or until centre is set.
Cool completely.
Cover and refrigerate at least 2 hours or overnight.
Sprinkle with icing sugar and garnish with remaining grated lemon peel, if desired, just before cutting into square to serve.
Store leftover squares in refrigerator.
