Sift first 6 ingredients into bowl.
Whisk oil, water, egg white and vanilla in separate bowl until combined. Add all at once to dry ingredients. Whisk just until combined.
Spread mixture onto parchment paper-lined half sheet pan to within 1 inch of edge. Sprinkle with OREO Pieces.
Bake in 350°F convection oven 20 to 22 min. or until firm. Remove from oven. Cool completely in pan on wire rack. Break into pieces to serve.