HEAT oven to 350ºF. Line 8-inch square baking pan with foil, with ends of foil extending over sides of pan; set aside. Mix crumbs, 1/2 cup flour and the brown sugar in bowl. Cut in margarine with pastry blender or 2 knives until mixture resembles coarse crumbs; press firmly onto bottom of prepared pan. Bake 15 min.

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. lemon peel, lemon juice and baking powder; pour over crust.

BAKE 25 to 28 min. or until centre is set. Cool completely. Cover and refrigerate at least 2 hours or overnight. Sprinkle with icing sugar and remaining 2 Tbsp. grated lemon peel just before cutting into squares to serve.