1. Sprinkle gelatin over cold water in small cup; let stand 2 minutes to soften. Add boiling water; stir until gelatin is completely dissolved and mixture is clear. Cool slightly, about 5 minutes.
2. Stir together sugar and cocoa in medium bowl; add whipping cream and vanilla. Beat on medium speed of mixer until stiff, scraping bottom of bowl occasionally. Add gelatin mixture; beat just until well blended. Pour into prepared pie crust.
3. Prepare MINT CREAM TOPPING; spread over filling. Refrigerate at least 2 hours. Cover; refrigerate leftover pie. 6 to 8 servings.
MINT CREAM TOPPING: Beat 1 cup (1/2 pt.) cold whipping cream, 2 tablespoons powdered sugar, 1/4 to 1/2 teaspoon peppermint extract and several drops green food color in medium bowl until stiff. About 2 cups topping.