Preheat oven to 350F degrees and grease 9x9 baking dish with coconut oil or cooking spray.
In a large mixing bowl, combine softened butter with oatmeal. Using a pastry blender (or knife and fork), cut the butter into the rolled oats until small (pea-sized) crumbles begin to form.
Slowly add in other crust/topping ingredients, continuing to cut the mixture into crumbles.
In a medium bowl, mix together filling ingredients.
Pour half of the crust/topping crumbles into the baking dish. Using a fork, press crumbles until packed tightly into the bottom of the dish.
Spread filling evenly over crust.
Pour the remaining half of the crust/topping crumbles over the filling. Similarly to the crust, using a fork, press crumbles until tightly packed.
Bake for 30 minutes.
Allow bars to cool before cutting, but may be served warm.