1. Finely grind crackers in food processor. Remove to bowl. Add butter; mix well.
2. Coat 9-inch springform pan with cooking spray; press crumbs into bottom. Bake at 350º for 10 minutes. Remove and cool.
3. Combine orange zest, juice, and liqueur in microwave-safe dish. Add gelatin; set aside, 10 minutes. Microwave on HIGH, 20 seconds.
4. Combine mixture and next 5 ingredients in bowl. Beat till smooth. Add 3 cups whipped topping; beat until color is uniform. Pour mixture into crust, cover; chill 3–4 hours. Serve with whipped topping and orange zest, if desired.