Mix the butter and brown sugar together in a bowl with an electric mixer. Then mix rolled oats, flour, salt and baking powder in another bowl.
Slowly add the dry to the wet while continually mixing. It will feel a little dry, but when you pack it into the pan it’ll be fine.
Mix together pumpkin, cool whip, vanilla extract and cinnamon in another bowl.
Grease a cupcake pan and pack some of the crust mixture into the bottom of each cupcake section. Only use about 3/4 the mixture on the bottom layer. (You can also use a 9x13 pan if you want it more like crunch bars, rather than individual portions)
Spoon a heaping spoonful of the pumpkin mixture into each cupcake section.
Crumble the remaining oat mixture over the tops of the sections.
Bake for about 25 minutes, or until the oats are starting to brown.