Cream sugar and butter in mixer on medium speed until fluffy. Add eggs, one at a time, until incorporated. Add the vanilla and beat well. Whisk together flour and baking powder. Turn mixer speed down to lowest setting and slowly add flour mixture until completely combined.
Spread half of mixture (I actually weight mine to get even halves, cuz I'm obsessive that way) onto an ungreased 15x10 jelly roll pan. Spread pie filling over the top of the batter. Drop remaining batter onto the pie filling layer by spoonfuls.
Bake for 45 minutes or until golden brown. Do not under bake. Remove to a wire rack.
Combine powdered sugar, melted margarine and lemon juice and drizzle over warm bars.
Allow to cool completely before cutting into squares.