Add Oreo cookies to a food processor and pulse until cookie is a fine crumb. Add 1 1/2 tablespoons sugar, salt, and melted butter to cookie crumbs; pulse until well combined. Press cookie mixture into a 9" pie plate until evenly distributed - the crust should go up the sides just a little. Bake for 12 minutes. Remove from oven and cool on a wire rack.
In a microwave safe bowl, heat 1 1/4 cups heavy cream for 3 minutes. Add chocolate to cream and allow to stand for 5 minutes. Whisk until chocolate and cream are smooth and completely integrated. Add rum, and whisk to combine. Pour chocolate mixture into pie crust. Top with nuts. Refrigerate for 3 hours (or up to 2 days).
In a large bowl, beat 2 cups heavy cream, 1 1/2 tablespoons sugar, and vanilla until stiff peaks form. Dollop whipped cream onto chilled pie and spread evenly to cover top of pie.