Preheat the oven to 375ºF and coat a cast-iron skillet or a baking dish with cooking spray or butter.
In a large mixing bowl combine the oats, flour, brown sugar, baking powder, baking soda, and pumpkin spice together until fully mixed.
Add the butter cubes to the oat mixture and use a pastry cutter or your hands to cut the butter into the mixture so it's coated completely and the pieces are small and pea-like in size.
Using about 4 cups of the mixture spread it over the bottom and sides of the skillet or baking dish. Press it down firmly.
In a separate large mixing bowl whisk the eggs and sugar together until smooth, but don't overmix.
Add the pumpkin puree, vanilla extract, heavy cream, pumpkin pie spice, and salt, and continue to whisk until the ingredients are smooth and fully incorporated.
Pour the pumpkin batter into the skillet or baking dish over the crisp bottom.
Sprinkle the remaining crisp over the pumpkin batter.
Bake for 45 to 50 minutes until the center is firm to touch. If the top begins to brown too much you can lightly cover it with foil.