Make the crust: Preheat the oven to 350 degrees F and butter a 9-inch pie plate. Pulse the chocolate wafers, sugar and orange zest in a food processor until finely ground. Add the melted butter and pulse to combine. Press the crumb mixture into the bottom and up the side of the prepared plate. Bake until set, 15 to 20 minutes, then transfer to a rack to cool completely.
Combine the chocolate and heavy cream in a small microwave-safe bowl and microwave in 30-second intervals, stirring after each, until smooth. Pour into the cooled crust and spread over the bottom and up the side; set aside until the chocolate sets, about 20 minutes.
Meanwhile, make the filling: Sprinkle the gelatin over 3 tablespoons water in a large bowl; let sit 5 minutes. Combine the milk, 2/3 cup sugar, the egg yolks, pumpkin, cinnamon, ginger and salt in a medium saucepan. Cook over medium-low heat, stirring, until the mixture bubbles, 6 to 8 minutes. Carefully whisk the milk mixture into the gelatin mixture until combined. Let sit at room temperature, stirring frequently, until cool but not set, 30 to 45 minutes.
Beat 3/4 cup heavy cream in a bowl with a mixer until soft peaks form. Gently fold the whipped cream into the cooled pumpkin mixture, then pour into the prepared crust. Press plastic wrap directly on the surface and refrigerate until firm, at least 3 hours or overnight.
Beat the remaining 1 cup heavy cream and 1/4 cup sugar until stiff peaks form. Spread on top of the pie.