Spray a 9x13-inch baking dish with non-stick cooking spray.
In a large mixing bowl, whisk together 3 large eggs, ½ cup brown sugar, and ½ cup granulated sugar until combined.
Stir in 1 can (15 ounces) pure pumpkin, 1 cup evaporated milk, 1 teaspoon vanilla extract, 1 teaspoon pumpkin pie spice, and 1 teaspoon ground cinnamon until the mixture is smooth.
Pour the pumpkin mixture into the prepared baking dish.
In a separate bowl, combine ¾ cup old-fashioned oats, 1 cup all-purpose flour, ½ cup brown sugar, ¼ teaspoon baking powder, 1 teaspoon ground cinnamon, and ½ cup butter. Mix until crumbly.
Sprinkle the oat mixture evenly over the pumpkin layer.
Bake for 35 to 40 minutes until the topping is golden brown and the filling is bubbly.
Remove from the oven and let the pumpkin crisp cool for 5 minutes.