Preheat the oven to 350 degrees.
Grease an 8x8 or 9x9 baking dish.
In a blender or in a mixing bowl add the pumpkin, sweetened condensed milk, eggs, pumpkin pie spice and cinnamon. Blend or mix until smooth and fully blended.
Pour the pumpkin mixture into the baking pan. Set aside.
In a bowl mix together the oatmeal, butter, brown sugar, butter, baking soda, salt, and baking powder.
Sprinkle the crumble over the pumpkin mixture. It's ok if some of the crumble sinks into the pumpkin.
Bake for 45-50 minutes or until it is set, and the center does not jiggle.
Serve slightly warm or room temperature with ice cream or whipped topping.
Refrigerate any leftovers.