01 - Preheat oven to 350°F. Grease a 9x13-inch baking dish with butter or nonstick cooking 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 the mixture is smooth and well combined. Pour the filling into the prepared baking dish and spread it 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 becomes crumbly and evenly moistened. Fold in the chopped pecans if using.
04 - Scatter the crisp topping evenly over the pumpkin filling, ensuring full coverage across the surface of the dish.
05 - Place the dish in the center of the oven and bake for 40 to 45 minutes, until the pumpkin filling is set and the topping is a deep golden brown.
06 - Remove from the oven and allow the dessert to cool for at least 20 minutes before slicing. Serve warm or chilled, optionally accompanied by whipped cream or a scoop of vanilla ice cream.