Place sherbet in bowl; stir until smooth. Stir in 1/2 of the cool whip until well blended (see note). Spoon into crust. Sprinkle with chopped Oreo cookies, pressing firmly into sherbet. Cover with remaining cool whip.
Freeze 4 hours or until firm. Let stand at room temperature 10 minutes before serving. Garnish with finely-chopped Oreo cookies and candy pumpkins, if desired.
* For more intense orange color, stir in a few drops each of red and yellow food coloring.