01 - Preheat the 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 smooth and well combined. Pour the filling into the prepared baking dish and spread it 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 stir until the mixture becomes crumbly and evenly moistened. Fold in the chopped pecans if using.
04 - Sprinkle the crisp topping evenly over the pumpkin filling, covering the surface as uniformly as possible.
05 - Bake for 40 to 45 minutes, or until the pumpkin filling is set and the oat topping is golden brown and crisp.
06 - Allow the crisp to cool for at least 20 minutes before serving. Serve warm or chilled, optionally topped with whipped cream or a scoop of vanilla ice cream.