Preheat oven to 350 degrees F (175 degrees C). Grease a 9x13-inch baking pan with cooking spray.

Mix pumpkin puree, evaporated milk, eggs, sugar, cinnamon, nutmeg, and allspice together in a large bowl. Spread into the prepared baking pan.

Stir cake mix and butter together in a large bowl. Stir in 1 cup pecans. Crumble evenly over the pumpkin mixture; pat down gently. Sprinkle remaining 1 cup pecans on top.

Bake in the preheated oven until a toothpick inserted into the center comes out clean and the top is a little crunchy, 45 to 55 minutes.