In a large bowl, combine 1 cup flour, oats and 1/2 cup brown sugar; cut in butter until crumbly. Press into a greased 13-in. x 9-in. baking pan. Bake at 375° for 8-10 minutes or until golden brown. Cool on a wire rack.
In a large bowl, beat eggs, vanilla and remaining brown sugar. Combine the coconut, walnuts, baking powder, salt and remaining flour; gradually add to egg mixture and mix well. Stir in chocolate chips.
Spread evenly over crust. Bake for 18-20 minutes or until golden brown. Cut into bars while warm. Cool on a wire rack.