Preheat oven to 350°F (175°C). Grease a 9×13-inch baking dish or pie dish.
In a large bowl, whisk pumpkin puree, evaporated milk, granulated sugar, brown sugar, eggs, vanilla, pumpkin pie spice, cinnamon, and salt until smooth.
Pour into the prepared baking dish.
In a medium bowl, combine flour, oats, brown sugar, and cinnamon. Stir in melted butter until crumbly. Mix in pecans if using.
Sprinkle the crisp topping evenly over the pumpkin filling.
Bake for 40-45 minutes, or until the topping is golden and the filling is set. A knife inserted into the center should come out mostly clean.
Allow to cool slightly. Optionally top with whipped cream or vanilla ice cream before serving.