Before you start, preheat the oven to 350 F
Line a 9-inch baking pan with parchment paper. Cut the parchment paper to be about 3 inches wider on each side of the pan. Cut slits on all corners, as long as the height of the pan, so the parchment paper covers the bottom of the pan, while also leaving overhangs on all sides to easily remove the dessert from the pan.
In a small bowl, combine flour, oatmeal, brown sugar, ground cinnamon and butter. It will be a crumbly mix that will hold together when you apply pressure.
Reserve about 1⁄2 cup of this mixture and add the rest to the prepared baking dish. Spread it around and press down lightly to make sure it forms a nice single layer of crust.
In a large bowl combine pumpkin puree, condensed milk, eggs and pumpkin pie spice. Mix well using a whisk. Whisk it till it is just about all incorporated together.
Pour this over the shortbread crust in the baking pan. Place in the oven for about 30 mins.
To the reserved shortbread crust mix, add the chopped pecans and mix well.
Remove the baking pan from the oven and sprinkle this all over the pumpkin custard in a single layer.
Put the baking pan back in the oven and bake for another 10 mins.
You will know it is ready when it still has a jiggle to it when you shake the pan but is firm to look at. Do a toothpick test to make sure it comes out clean.