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