Make crust. Pulse Oreos into fine crumbs, combine with butter, press into an 8" pie pan, then chill.
Prepare orange filling. Dissolve Jell‑O and extract in boiling water. Add orange juice and ice to partially set. Fold in whipped topping when cooled.
Layer filling & fruit. Pour half the filling into crust, arrange mandarin segments, pour remaining filling. Chill until firm (~30 min).
Make ganache. Heat cream; pour over chocolate chips; let sit, then stir smooth. Cool slightly.
Top pie. Pour ganache over set pie carefully. Let flow evenly.
Chill fully. Refrigerate for ≥4 hours or overnight.
Decorate & serve. Pipe edges with ganache, top with mandarin slices, and slice with sharp knife.