Create the chunky texture by leaving those extra-big blueberry-size pieces in the streusel mix.
Preheat oven to 350°. Sprinkle work surface with powdered sugar. Unroll piecrust, and place on prepared surface. Sprinkle piecrust with chopped pecans. Place wax paper over piecrust and pecans, and lightly roll pecans into crust. Fit piecrust, pecan side up, in a lightly greased (with cooking spray) 9-inch pie plate; fold edges under, and crimp.
Whisk together pumpkin and next 6 ingredients in a large bowl until smooth and well incorporated; pour into prepared piecrust.
Bake at 350° for 45 minutes, shielding edges with aluminum foil after 20 minutes, if needed, to prevent excessive browning. Carefully top pie with Pecan Streusel Topping. Reduce oven temperature to 325°, and bake 25 minutes, covering pie with aluminum foil after 5 to 10 minutes to prevent excessive browning. Cool completely on a wire rack (about 2 hours).
Pecan Piecrust How-to
1 Unroll piecrust onto a surface dusted with powdered sugar; sprinkle with chopped pecans.
2 Place a sheet of wax paper over piecrust and pecans, and gently roll, pressing pecans into crust.
3 Fit piecrust, pecan side up, in a lightly greased pie plate. Fold the edges under, and crimp.