In a mixing bowl, combine graham cracker crumbs, melted butter, and sugar. Press firmly into a greased 9×13-inch baking dish. Bake at 350°F (175°C) for 10 minutes, then let cool.
Beat cream cheese until smooth. Add pumpkin puree, brown sugar, eggs, vanilla, cinnamon, and nutmeg. Mix until fully combined.
Pour the cheesecake filling evenly over the cooled crust. Sprinkle crushed pecans on top.
Return to the oven and bake for 30–35 minutes, or until the filling is set.
Let cool at room temperature for 30 minutes, then refrigerate for at least 2 hours.
Slice into bars and top with whipped cream if desired.