Heat oven to 350°F.
Spray 15x10x1-inch pan with cooking spray. Line with waxed paper; spray with additional cooking spray.
Microwave 3 oz. chocolate and butter in medium microwaveable bowl on High 1-1/2 to 2 min. or until butter is melted. Stir until chocolate is completely melted. Add granulated sugar; mix well. Beat eggs in large bowl with mixer on high speed 3 min. or until thickened. Blend in chocolate mixture. Add 1/4 cup flour and baking soda; beat just until blended. Add remaining flour alternately with water, beating well after each addition. Spread evenly into prepared pan.
Bake 15 min. or until top of cake springs back when touched; sprinkle with 1/4 cup powdered sugar. Immediately invert cake onto clean towel; remove pan. Carefully peel off paper. Starting at one short side, roll up cake and towel together; cool completely on wire rack.
Beat cream cheese and remaining powdered sugar in medium bowl with mixer until well blended. Gently stir in 1-1/2 cups COOL WHIP.
Unroll cake carefully; remove towel. Spread cream cheese mixture onto cake, completely covering top of cake. Roll up cake; place, seam-side down, on platter.
Microwave remaining chocolate and remaining COOL WHIP in microwaveable bowl on HIGH 1 to 1-1/2 min. or until chocolate is completely melted and mixture is well blended, stirring after 1 min. Cool 2 min.; spread onto cake. Refrigerate 1 hour.