Beat pudding mix and milk in large bowl with whisk 2 min. Add pumpkin and spice; mix well. Let stand 5 min.
Meanwhile, cover bottom of 13x9-inch pan with 9 crackers, breaking as necessary to form even layer.
Add 2 cups COOL WHIP to pudding; whisk just until blended. Spread half the pudding mixture over crackers in pan; cover with half of the remaining crackers. Repeat layers of pudding and crackers. Refrigerate 3 hours.
Microwave remaining COOL WHIP and chocolate in microwaveable bowl on HIGH 1 min. or until chocolate is completely melted and mixture is well blended when stirred; spread over dessert. Refrigerate 15 min.