HEAT oven to 350ºF.
MIX cookie crumbs, sugar and butter; press onto bottom of 8-inch square pan. Bake 10 min. or until lightly browned; cool completely.
BRING nectar to boil. Add to gelatin mixes in large bowl; stir 2 min. until completely dissolved. Beat with mixer on high speed 5 min. or until frothy and opaque.
BLEND milk and mangos in blender until smooth; whisk into gelatin mixture. Stir in 1 cup COOL WHIP; pour into crust. Refrigerate 2 hours or until firm. Serve topped with remaining COOL WHIP.