PREHEAT oven to 375º F. Grease a 9-inch-square baking pan.
COMBINE flour, oats, granulated sugar, brown sugar, baking powder and salt in large bowl. Cut in butter with a pastry blender or two knives until crumbly; reserve 3/4 cup oat mixture for topping. Press remaining oat mixture into prepared baking pan. Spread preserves over crust; sprinkle with chunks.
COMBINE reserved oat mixture and nuts; sprinkle over chunks. Pat down lightly.
BAKE for 30 to 35 minutes or until golden brown. Cool completely in pan until chocolate is firm, or refrigerate for 30 minutes to speed cooling. Cut into squares.