Combine first 6 ingredients. Stir well; set aside.
Cream margarine in a large bowl; gradually add brown sugar, beating at medium speed of a mixer until light and fluffy. Add egg; beat well. Add flour mixture to creamed mixture; beat just until dry ingredients are moist. Stir in vanilla, apple, oats, and currants.
Spoon batter into a 9-inch square baking pan coated with cooking spray.
Bake at 350° for 40 minutes or until a wooden pick inserted in center comes out clean. Cool completely in pan on a wire rack. Sprinkle powdered sugar over top.