Preheat oven to 350 degrees and prepare a baking dish with cooking spray.
Combine all of the filling ingredients and evenly distribute into your baking dish.
To make the topping, simply combine the flour, brown sugar, and cinnamon with a whisk.
Using a pastry blender or two forks, cut the vegan margarine into the flour mixture until it resembles coarse crumbs. Add the oats (and nuts, if using). Sprinkle over the filling.
Bake for about 40 minutes or until the topping is golden and the juices are bubbling.