In a large bowl, whisk together pumpkin, evaporated milk, brown sugar, eggs, and pumpkin pie spice. Pour the batter into a 9 by 13-inch baking dish coated with cooking spray.
Sprinkle cake mix evenly over the top of the pumpkin mixture. Then sprinkle on the crushed graham crackers and chopped pecans.
Drizzle melted butter over the top of the batter, trying to evenly coat the ingredients with butter.
Bake in the preheated oven for 45 to 50 minutes, until center is set and topping is nicely browned.
Scoop out by spoonfuls and serve topped with ice cream if desired.
Notes
Nutrition facts are estimates and don't include ice cream.