Preheat oven to 350°. Bake pecans in a single layer in a shallow pan 8 to 10 minutes or until toasted and fragrant, stirring halfway through. Cool 10 minutes.
Stir together graham cracker crumbs, next 2 ingredients, and toasted pecans until blended. Press crumb mixture on bottom, up sides, and onto lip of a lightly greased 10-inch pie plate.
Bake at 350° for 10 to 12 minutes or until lightly browned. Transfer to a wire rack, and cool completely (about 30 minutes).
Microwave 1 cup semisweet chocolate morsels and 1/2 cup whipping cream in a small microwave-safe bowl at HIGH 1 minute or until melted, stirring at 30-second intervals. Spoon chocolate mixture over bottom of pie crust; sprinkle candy bars over chocolate mixture. Cover and chill 1 hour or until chocolate mixture is set.
Meanwhile, whisk together sugar and flour in a heavy 3-qt. saucepan; add eggs, egg yolks, and milk, and whisk until blended. Cook over medium heat, whisking constantly, 8 to 10 minutes or until a pudding-like thickness. (Mixture will just begin to bubble and will hold soft peaks when whisk is lifted.) Remove from heat, and whisk in pumpkin and vanilla bean paste. Transfer to a bowl. Place heavy-duty plastic wrap directly on warm filling (to prevent a film from forming); chill 30 minutes. Spoon pumpkin mixture over chocolate; cover and chill 8 to 24 hours or until filling is firm.
Beat remaining 1 1/2 cups cream at high speed with an electric mixer until foamy; gradually add syrup, beating until soft peaks form. Spread or pipe over pie.