In a large bowl, combine 2-½ cups flour, oats, sugar, baking powder and cinnamon. Beat in butter just until moistened. Set aside 2 cups for topping.
Pat remaining oat mixture into a greased 13-in. x 9-in. baking pan. Bake at 375° for 15 minutes.
In a large bowl, toss apples with remaining flour; stir in the preserves. Spread over hot crust to within ½ in. of edges. Combine nuts and reserved oat mixture; sprinkle over fruit mixture.
Bake 30-35 minutes longer or until lightly browned. Cool completely on a wire rack. Cut into bars.
