Combine the filling ingredients in a mixing bowl and set aside.
Process ½ cup of the oats in a food processor until it forms a coarse flour.
In a small bowl, combine the oat flour with the remaining ½ cup of oats and the rest of the crumble topping ingredients. Mix until well combined.
Spoon the filling into a 24 ounce baking dish.
Spread the crumble topping over the filling.
Bake for 30 to 40 minutes until heated through and lightly browned on top.
Leftovers can be covered and refrigerated for 3 to 4 days. Reheat in a microwave or oven or enjoy at room temperature.You can also make this dessert in advance. Bake it as stated in the recipe, then cover and reheat it when you're ready to serve.