01 - Preheat the oven to 350°F. Grease a 9x13-inch baking dish with butter or nonstick spray.
02 - In a large mixing bowl, whisk together the pumpkin purée, eggs, evaporated milk, granulated sugar, cinnamon, nutmeg, ginger, cloves, salt, and vanilla extract until completely smooth. Pour the filling into the prepared baking dish and spread into an even layer.
03 - In a separate bowl, combine the rolled oats, all-purpose flour, packed brown sugar, and cinnamon. Pour in the melted butter and stir until the mixture forms coarse, crumbly clusters. Fold in the chopped pecans if using.
04 - Scatter the crisp topping evenly over the pumpkin filling. Bake for 40 to 45 minutes until the filling is set and the topping is deep golden brown.
05 - Allow the dessert to cool for at least 20 minutes before slicing. Serve warm or chilled, topped with whipped cream or a scoop of vanilla ice cream if desired.