Break up 14 full-size graham cracker sheets into large pieces and place in a food processor. Add 1 ¼ cups coarsely chopped pecans, 1 tablespoon packed brown sugar, ¾ teaspoon ground cinnamon, and ¼ teaspoon kosher salt. Pulse until the mixture resembles coarse sand and some pecan pieces are still visible, 18 to 20 (1-second) pulses.

Melt 1 stick unsalted butter in a large skillet over low heat. Add the graham cracker mixture and cook, stirring frequently, until the mixture is toasted and fragrant, 2 to 3 minutes. Remove the skillet from the heat.

Coat a 9x13-inch baking pan with cooking spray. Line the bottom and two long sides of the pan with a sheet of parchment paper long enough to extend over the edges by at least 2 inches to form a sling.

Transfer the graham cracker mixture into the baking pan and press evenly into the bottom of the pan with the bottom of a flat measuring cup. Refrigerate while you prepare the filling.

Beat 2 cups cold heavy cream, 3 tablespoons maple syrup, and 1 teaspoon vanilla extract together in a stand mixer with the whisk attachment on medium speed until soft peaks form, about 2 to 3 minutes. Transfer to another bowl.

Beat 24 ounces very soft cream cheese (microwave for 10 seconds if needed so that it is spreadable), 1 (15-ounce) can pumpkin purée, 2 cups powdered sugar, 1 teaspoon ground cinnamon, ½ teaspoon ground ginger, and ½ teaspoon ground nutmeg together in the stand mixer (no need to clean) with the whisk attachment on medium speed until well-combined and only very small lumps are visible, about 30 to 45 seconds.

Add the whipped cream and gently fold together by hand with a flexible spatula until fully incorporated and no streaks of whipped cream remain.

Transfer onto the crust and spread into an even layer. Refrigerate until set, at least 4 hours or up to overnight.

Beat 1 ½ cups cold heavy cream, 3 tablespoons maple syrup, and ½ teaspoon vanilla extract together in a stand mixer with the whisk attachment on medium speed until medium peaks form, about 2 minutes.

Grasping the excess parchment, lift the slab out of the baking pan and place on a cutting board. Cut into 16 pieces, wiping your knife clean between each cut or as needed. Serve topped with the maple whipped cream, garnished with chopped toasted pecans and dusted with ground cinnamon if desired.