Preheat oven to 350°F.
Grease a deep square pan or a 2-3 qt casserole dish.
In a large bowl, whisk together all of the filling ingredients; pour into the prepared dish.
1 15-ounce can pumpkin puree, 2/3 cup sugar, 1 5-ounce can evaporated milk, 3 eggs, 1 teaspoon vanilla extract, 2 teaspoon pumpkin pie spice, 1/4 teaspoon salt
In a medium bowl, combine the gingersnap cookie flour*, oats, brown sugar, soda and powder. Then, use a fork to incorporate the butter into the dry mixture.
1 cup Gingersnap cookie "flour"*, 1 cup quick oats, 1/3 cup brown sugar, 1/4 teaspoon baking soda, 1/4 teaspoon baking powder, 1/2 cup butter
Evenly sprinkle the topping over the pumpkin filling.
Bake for 35-45 minutes, or until the center of the pumpkin pie filling reaches 175°F. The center will still have a little wiggle, but it won't be super runny.
Serve with ice cream or whipped topping, if desired.